In July 2015, police officers stopped Javier Ayala for driving a vehicle with a suspended license. During a search of his vehicle and a subsequent search of his home under a previously issued warrant, officers found a .22-caliber pistol and 1,286 bags of heroin. The net weight of the bags' contents was approximately 15 grams. In separate trials, two juries convicted Ayala of multiple charges relating to the contraband police found in Ayala's home and vehicle. Because Ayala had been previously convicted of four other felonies, the Superior Court declared Ayala to be a habitual offender under 11 Del. C. § 4214 and sentenced him to a mandatory minimum prison term of seven years and six months.
On appeal, Ayala challenges his convictions and sentence on two grounds. First, he contends that the Superior Court abused its discretion when it admitted evidence regarding the identity and weight of the substance in the bags seized from his home and vehicle because the chemist who tested the suspected heroin bags did not lay a proper foundation for the admission of her hypergeometric-testing results. Second, Ayala argues that, as a matter of law, he should not have been adjudged a habitual offender because the offenses forming the basis of three of his predicate felony convictions were no longer felonies when he was sentenced in this case.
We have concluded that the chemist's testimony regarding her testing procedures, while less than ideal, was not so deficient as to render the admission of the testing results an abuse of the Superior Court's discretion. And despite the General Assembly's reform of our drug laws in 2011 such that three of Ayala's predicate felony convictions are no longer felonies and no longer defined as distinct offenses, Ayala is nevertheless subject to sentencing as a habitual offender under 11 Del. C. § 4214 because he had been three times convicted of a felony and was thereafter-in this case-convicted of a subsequent felony.
I. BACKGROUND
On July 27, 2015, Wilmington Police were conducting surveillance on 1002 Sycamore *831Street. They suspected that Ayala lived there and that he was dealing drugs. Accordingly, police had obtained a search warrant for 1002 Sycamore Street.
While surveilling the home, police officers saw Ayala leave the residence and drive away in a minivan. Because the officers knew that Ayala's driver's license was suspended, they stopped him on a nearby street. The officers searched the car and found a bundle of 50 bags of individually packaged suspected heroin doses in the passenger compartment of the minivan near the center console.
The officers then took Ayala to their headquarters and called additional officers to conduct the search of 1002 Sycamore Street. Inside 1002 Sycamore Street, officers found another, larger bundle containing 1,236 bags of suspected heroin and a .22-caliber semiautomatic pistol. At headquarters, Ayala admitted that the bundles of heroin and the gun were his and that he intended to sell the heroin.
The police turned the seized drugs over to the Delaware Division of Forensic Science ("DFS") for forensic testing. The task of testing the evidence against Ayala was assigned to Ashley Wang, a forensic chemist at DFS. After conducting a series of tests using a process called "hypergeometric testing," Wang issued a report indicating that she was confident that the bags police seized from Ayala contained heroin and so testified at trial.
Ayala was indicted on charges of Drug Dealing, Aggravated Possession of Heroin, Driving a Vehicle While License is Suspended or Revoked, Possession of a Firearm by a Person Prohibited, Possession of Ammunition by a Person Prohibited, and Endangering the Welfare of a Child. Ayala was tried in two separate trials after the Superior Court granted his motion to sever the person-prohibited and child-endangering charges1 and was convicted on all counts.
Before sentencing, the State moved to declare Ayala a habitual offender. The Superior Court granted the State's motion and sentenced Ayala to a mandatory minimum of seven-and-one-half years' imprisonment on the possession-of-a-firearm-by-a-person-prohibited offense, followed by suspended terms of imprisonment on the remaining criminal offenses, and a fine on the traffic offense, among other punishments. Ayala timely appealed his conviction and sentence to this Court.
On appeal, Ayala argues that the Superior Court abused its discretion when it admitted Wang's testing results. Ayala contends that, because Wang could not remember how she randomly selected her samples, her results lacked a proper foundation and should not have been admitted. Ayala also contends that he should not have been adjudged a habitual offender. We address both contentions in turn, but first we review the nature of hypergeometric testing and Wang's testing procedures in Ayala's case.
A. Overview of hypergeometric testing
Essentially, hypergeometric2 testing randomly selects a small sample from a *832larger population, tests that sample, and extrapolates the sample results to the larger population. Hypergeometric testing is based on the frequentist approach to statistics.3 As applied to the testing of suspected controlled substances, "[t]he assumption behind a frequentist approach is that a fixed but unknown proportion of the seizure contains drugs. The proportion of drugs in ... the sampled units[ ] can estimate this seizure proportion. The proportion of drugs in the sample will, however, vary over different samples. Therefore, the frequentist methods provide a confidence ... that with a given sample proportion," drugs constitute some particular proportion of the entire seizure.4 For example, after hypergeometric testing of a drug seizure, a chemist may be able to infer-as Wang did here-that at least 90% of that drug seizure contains drugs at a 95% "confidence level."5
When performing hypergeometric testing of a batch of drugs, the chemist first separates the seized items (here, the suspected heroin bags) into externally homogeneous groups, or "populations."6 Next, the chemist counts the number of individual units within each population and uses a table based on the hypergeometric distribution to determine the appropriate number of samples to test from that population. The chemist then randomly selects that number of samples from the population *833to test. Finally, the chemist conducts the relevant tests and extrapolates the sample results to the population.
The randomness of the samples is crucial.7 Each unit in the population must have an equal chance of being selected for the samples to be a true reflection of the properties of the population.8 Arbitrary, nonstandardized methods of selecting samples lend themselves to error.9 For example, "it happens that sometimes the expert tends to choose similar sized units."10 It follows, then, that a reliable hypergeometric test requires a reliable method of randomly selecting the samples.
B. Wang's procedures and testimony
Wang testified on voir dire that, although she had no specific recollection of performing the random selection of samples and did not record her exact testing procedures in her written report in Ayala's case, her usual protocol is to sort and separate the drug seizure into homogeneous populations by appearance and provenance. She next weighs each population in a weigh boat. Then, she dumps the populations onto her lab bench into separate piles. Wang then refers to a testing manual for the appropriate number of samples to draw and test from each population. Wang could not recall how she drew the samples in Ayala's case-she said she had "no specific procedure."11 But it appears that she unsystematically-Wang insists that it was randomly and in accordance with the way she does it in every case12 -drew the requisite number of samples from the piles that she had dumped out. As mentioned, Wang eventually tested 62 of the 1,286 bags seized and detected heroin in every sample. She concluded that that "there is a 95% likelihood that at least 90% of the [seizure] submitted contain [heroin]"13 and that the net weight of the entire drug seizure was approximately 15 grams.14
Ayala sought to exclude Wang's conclusion on the grounds that the State had not offered sufficient evidence that Wang's methods ensured the homogeneity of each testing population or the randomness of *834the tested samples, and thus the foundation for her testimony was insufficient. The Superior Court disagreed with Ayala's contention that this foundational testimony regarding Wang's random selection of samples was insufficient and permitted Wang to testify.
II. AYALA'S EVIDENTIARY OBJECTION
A. Ayala's challenge
On appeal, Ayala makes two related arguments relating to Wang's random selection. According to Ayala, Wang's inability to remember how she randomly selected the samples for her hypergeometric tests rendered her testimony unreliable. Furthermore, according to Ayala, the Superior Court erred by reasoning that, because Wang's groupings were sufficiently homogeneous, the importance of the precise method of random selection was diminished. Such reasoning, Ayala contends, impermissibly eliminated the requirement of random selection from hypergeometric testing as a practical matter.
Ayala appears to maintain only his challenge to the sufficiency of Wang's random selection procedure and, in particular, her inability to recall her actual performance; he does not challenge the validity of properly conducted hypergeometric testing. Therefore, we do not address hypergeometric testing's general validity or admissibility, but only whether-assuming that the results of properly conducted hypergeometric testing are admissible-the State laid a sufficient foundation for the admission of Wang's opinion.
B. Evidentiary standards and standard of review
Under Delaware Rule of Evidence 702, an expert witness may give opinion testimony if "the testimony is based on sufficient facts or data; the testimony is the product of reliable principles and methods; and the expert has reliably applied the principles and methods to the facts of the case."15 When courts evaluate preliminary questions on evidence such as whether evidence is admissible, they are not subject to ordinary rules of evidence and may evaluate evidence otherwise not admissible.16
In determining whether expert testimony on a scientific, technical, or other specialized matter is admissible, the trial judge acts as a gatekeeper.17 The trial judge does not assess weight or credibility per se ,18 but only whether the proponent has demonstrated, by a preponderance of the evidence, that the proffered testimony is relevant and sufficiently reliable.19 As the Third Circuit Court of Appeals has stated, "the grounds for the expert's opinion merely have to be good[;] they do not have to be perfect."20 And "trial courts should hesitate to exclude evidence ... based on questions as to [reliable application] that are within the jury's ability to understand."21 Accordingly, admission of expert witness testimony requires reliability, not infallibility.22
*835Relatedly, the proper conduct of scientific testing rests on three elements: (1) that all instruments used were in proper working order; (2) that proper procedure was followed; and (3) that the test was conducted by qualified individuals.23 As noted, Ayala does not challenge the admissibility of properly conducted hypergeometric testing, nor does he challenge the condition of Wang's instruments or Wang's qualifications. Accordingly, we examine only whether the State sufficiently established that Wang in fact conducted the testing properly.24 Finally, because this is a ruling concerning the admissibility of expert witness testimony, we will reverse only if we find abuse of discretion.25
C. Wang's lack of recollection did not fatally undermine the foundation for her testimony
As mentioned, Wang had no independent recollection of performing the random selection of the suspected heroin bags after separating the seized bags into homogeneous populations. Instead, she described the standard way that she routinely performs this part of the testing process and confirmed that she always follows that routine. Relying on our holding in Fensterer v. State ,26 Ayala argues that Wang's inability to remember her exact procedures fatally undermines her testimony. We disagree. In Fensterer , we held that Rule 705 of the Delaware Uniform Rules of Evidence did not permit the admission of the testimony of an FBI special agent who could not remember which of three potential observations he made formed the basis of his conclusion that a victim's hair had been forcibly removed.27
But here, the issue is not that Wang could not remember what observations she made. Wang's observations, i.e. , the weight and contents of the tested bags, were recorded and made part of the trial record. Those observations were the basis of Wang's conclusion that the police had seized 15 or more grams of heroin. The question that Ayala raises is whether, in light of Wang's inability to specifically recall her performance of the testing in this case, the trial court could make the preliminary determination that those observations were formed in a sufficiently reliable way, which simply was not the question in Fensterer . On this key point, the State provided evidence of Wang's usual testing procedure. And in the absence of evidence to the contrary, it was reasonable for the trial judge to infer that Wang followed her usual procedure despite her inability to recall her particular actions in Ayala's case.28 Accordingly, we do not think that Wang's memory lapse so undermined the foundation of her testimony that it was rendered inadmissible.
Moreover, we agree with the Superior Court's observation that the precise manner *836in which random selection is performed is of diminished importance, where, as here, there has been a threshold showing of the homogeneity of the population to the trial judge acting as gatekeeper. The recommendations for well-defined random-selection procedures are based on the concern that, if the tested population is not truly homogeneous, the technician might choose samples that, based on outward appearance, are more or less likely to contain contraband than the population as a whole. Where the population is truly homogeneous and previously randomly shuffled (as dumping all the bags onto a lab table before selecting the sample group would tend to do), then the random selection method would necessarily be less likely to affect testing reliability.29
Finally, although on appeal Ayala does not mount a frontal attack on Wang's usual procedures for ensuring population homogeneity and randomly selecting samples, choosing instead to focus on Wang's lack of specific recall of how she performed those steps in this case,30 the adequacy of Wang's procedures warrant brief consideration here.
It is well-established that humans are not naturally skilled at judging and producing randomness,31 and in the field of hypergeometric testing there appear to be preferred methods for ensuring that the selection of samples is in fact random.32 Indeed, the widely accepted guidelines for hypergeometric testing published by the European Network of Forensic Science Institutes suggest two methods for conducting a random selection.33 The first entails numbering each item in the population to be tested and then using a computer to generate a set of random numbers to choose the samples for testing. The second-known as the "black box" method-entails placing the population in a box and having the experimenter blindly draw a set of items from that box. But those guidelines do not mandate either the numerical or the black-box method for random sampling; what is necessary is simply some reliable method for producing randomness that is not subject to the well-documented fallibilities and foibles of the human experimenter.
Here, we conclude that Wang's failure to use a recommended method for random selection in this case-a practice apparently blessed by DFS-was not fatal to the admission of her testimony. Although we have excluded evidence for failure to follow proper testing procedure, in those cases the defendant showed that the State violated unambiguous manufacturer instructions for producing reliable test results.34 Ayala *837has only produced non-binding guidelines that themselves state that other methods can produce sufficient randomness for reliable test results. He has not produced any affirmative evidence that Wang's methods seriously undercut the reliability of her results. Given the lack of established rules regarding random selection, the weaknesses in Wang's testimony did not go to the testimony's admissibility, but rather to its weight, which is a question for the jury.35 It bears repeating that, as a gatekeeper, the trial court is looking for reliability, not infallibility.
In addition, proper hypergeometric testing procedure requires separation of the drug seizure into homogeneous groups for sampling. For example, a seizure containing bags of similar size but with half labeled "Jaguar Blue" and the other half labeled, say, "Jaguar Red" should be separated into two groups for testing so that the testing can determine the characteristics of each group.36
We cannot say that Wang's testimony in this area did not give us pause. For instance, Wang admitted to grouping together bags that looked different, with what was suspected to be heroin visible in some bags and hidden in others by the packaging. Wang dismissed these differences by saying that the packaging material was identical even if there were differences in the way the alleged heroin was placed in the packaging and that those latter differences are immaterial. We understand, however, that visible differences in the bags' contents are relevant to their homogeneity or lack thereof, and bags with visible differences should be sorted into separate groups.
Nevertheless, although Wang could not specifically recall separating the seized bags into homogeneous groups in this case, she did note that her usual practice, which she says she follows in every case, is to examine each bag individually to ensure that there is a powder inside that is consistent with the others in the population. Such a practice can mitigate the risk of heterogeneity. Moreover, there was nothing in Wang's testing results that suggested that her groups were anything but homogeneous.
Ultimately, while Wang's procedures and foundational testimony might not have been flawless, the State made an adequate showing that Wang's results were reliable enough for admission. In sum, we conclude that the Superior Court did not abuse its discretion when it admitted Wang's testimony.
III. AYALA'S HABITUAL OFFENDER STATUS
Ayala also challenges the Superior Court's finding that he was a habitual offender under § 4214 and therefore subject to enhanced sentencing. Ayala says that this finding was erroneous because Delaware *838recategorized37 several of the predicate felonies that the Superior Court used to determine that he was a habitual offender. Because this question involves the application of law to undisputed facts, our review is de novo .38
A. Ayala's previous convictions and § 4214's sentencing enhancements
Under the version of 11 Del. C. § 4214 that the Superior Court applied to Ayala, "any person who has been 3 times convicted of any felony under the laws of this State ... and who shall thereafter be convicted of a subsequent felony is declared to be a[ ] habitual criminal" and is subject to enhanced sentences.39 In particular, if the offender's subsequent felony is a violent felony as defined in 11 Del. C. § 4201(c), the offender is subject to a "minimum sentence of 1/2 of the statutory maximum penalty ...."40 Under § 4201(c), both possession of a firearm by a person prohibited and possession of ammunition by a person prohibited qualify as violent felonies, and therefore Ayala was subject to enhanced sentencing if he had three prior felony convictions. Prior to his 2015 arrest, Ayala had been convicted of four felonies:
• Possession with intent to deliver cocaine (1993)41
• Possession of a controlled substance within 300 feet of a park ("possession near a park") (1999)42
• Use of a dwelling for keeping controlled substances ("maintaining a dwelling") (2009)43
• Use of a dwelling for keeping controlled substances (2011).44
In 2011, Delaware enacted the Ned Carpenter Act.45 The Act eliminated the offenses of possession near a park46 and maintaining a dwelling47 but did not apply *839retroactively to any violation that occurred prior to September 1, 2011.48
On appeal, Ayala argues that because possession near a park and maintaining a dwelling were no longer felonies at the time of his sentencing, he should not be subject to § 4214's sentencing enhancements. The State replies that because Ayala's predicate acts were felonies when Ayala was convicted of those predicates, it is irrelevant that Delaware later recategorized such offenses or eliminated them as discrete offenses altogether.
B. Section 4215A
The State and Ayala both contend that 11 Del. C. § 4215A support their positions that Ayala is and is not subject to enhanced sentencing, respectively. In our opinion, however, § 4215A supports neither position and is inapposite to Ayala's sentencing.
Section 4215A, which is entitled "Sentence of greater punishment because of previous conviction under prior law or the laws of other jurisdictions," states in relevant part:
[A] previous conviction shall make the defendant liable to ... greater punishment if that previous conviction was ... [f]or an offense specified in the laws of this State or for an offense which is the same as, or equivalent to, such offense as the same existed and was defined under the laws of this State existing at the time of such conviction.49
We think the only sensible way to read § 4215A is as follows:
A previous conviction shall make the defendant liable to greater punishment if that previous conviction was [1] for an offense [currently] specified in the laws of this State or [2] for a [previously specified] offense which is the same as, or equivalent to, [a currently specified] offense as [that] same [previously specified offense] existed and was defined under the laws of this State existing at the time of [the previous] conviction.
In other words, we think that § 4215A says that a previous conviction makes the defendant subject to enhanced sentencing for his current conviction if his previous conviction was either (1) for an offense still specified as an offense at the time of sentencing or (2) for an offense that is "the same as, or equivalent to" an offense still specified as an offense at the time of sentencing.
Ultimately, § 4215A is irrelevant to Ayala's case because it is a non-exclusive provision that permits enhanced sentences when a person has been previously convicted of offenses still specified under the Delaware Criminal Code as offenses, or when they have been previously convicted of an offense that has a "same" or "equivalent" analog under current law, neither of which is the case here. We therefore agree with the Superior Court's conclusion that § 4215A provided "no aid" to Ayala.50
But we also reject the State's contention that § 4215A dictates that Ayala's possession-near-a-park and maintaining-a-dwelling convictions are predicate felonies in this case. It bears noting here that in the Superior Court, the State explicitly argued that " § 4215A... is not applicable under these circumstances."51 The Superior *840Court implicitly agreed,52 and for the reasons stated above, we also agree.53
C. Section 4214
Instead of relying on the relatively obtuse language of § 4215A, which, as noted, does not address the scenario presented in this case, we employ a straightforward application of § 4214 to reach the same result as the Superior Court. As noted above, § 4214 renders "any person who has been 3 times convicted of any felony under the laws of this State" subject to habitual offender status and enhanced sentencing.54 Ayala undeniably had been convicted three times of Delaware felonies. Indeed, when asked during oral argument, Ayala's attorney agreed that Ayala satisfied § 4214's enumerated requirements:
Q: ... 4214(b) applies to persons who have been three times convicted of a felony under the laws of this state. Does that accurately describe your client at the time of the triggering conviction?
A: It does, your honor.55
The unambiguous language of § 4214 compels the conclusion that the Superior Court correctly declared Ayala a habitual offender and correctly imposed a mandatory minimum sentence.
IV. CONCLUSION
Because the Superior Court did not abuse its discretion in admitting Wang's hypergeometric testing results and properly applied the enhanced sentencing provisions of 11 Del. C. § 4214, the judgment of the Superior Court is affirmed.