This case presents a dispute about how to calculate one of the variables used to measure the capacity a worker loses as the result of a compensable injury. We conclude that we are unable on this record to determine whether the Workers’ Compensation Board made the proper calculation. We reverse the Board’s order and remand for reconsideration.
The amount of compensation that an injured worker receives for a permanent injury depends on the extent of the disability (called “permanent partial disability,” or PPD) caused by the injury. ORS 656.214(5). The extent of disability, expressed as a percentage ie.g., “14 percent PPD”), depends in turn on the seriousness of the injury “as modified by factors of age, education and adaptability to perform a given job.” ORS 656.726(4)(f)(A). The Department of Consumer and Business Services provides formulas for expressing these modifying factors as numbers. A high number adds to the extent of disability, which, in turn, adds to the injured worker’s compensation.
The modifying factor at issue in this case is “adaptability.” Adaptability, under the Department’s rules, is determined by comparing the worker’s ability to perform work before and after the injury or, in the language of the rules, by comparing the worker’s “base functional capacity” (BFC) with his or her “residual functional capacity” (RFC). Former OAR 436-35-310(2) (1994).1 These statutes and rules reflect the proposition that a worker whose injury causes a significant loss of working capacity deserves more compensation than a worker whose injury inflicts minimal harm to working capacity, even if both workers end up identically disabled.
In this case, claimant worked as a certified nursing assistant for employer South Hills Health Care Center. While at work on May 11, 1993, she was injured when she fell. Her employer’s insurer, SAIF, accepted her workers’ compensation claim and paid for chiropractic treatment. A year after her injury, claimant became medically stationary. *16Her claim was subsequently closed by a determination order that concluded that she had not suffered any PPD. She requested reconsideration and, after an evaluation by a medical arbiter, was awarded 14 percent PPD. On review by the hearings division, an administrative law judge (AU) increased the award to 31 percent. Claimant then appealed to the Board, arguing that the AU erred in classifying her pre-injury capability as “medium” instead of “heavy.” The Board rejected her argument but, based on findings not relevant to this case, raised claimant’s PPD from 31 percent to 37 percent. Claimant sought review before this court, arguing that the Board had erroneously refused to consider testimony regarding the nature of her job at the time of her injury. We agreed with her argument and remanded to the Board for reconsideration. Fister v. South Hills Health Care, 149 Or App 214, 942 P2d 833 (1997), rev den 326 Or 389 (1998).
On reconsideration, the Board considered the evidence that was the subject of claimant’s first request for judicial review. It awarded claimant unscheduled disability of 45 percent. It observed,
“Adaptability is measured by comparing a worker’s Base Functional Capacity (BFC) to the Residual Functional Capacity (RFC) at the time of becoming medically stationary. Former OAR 436-35-310(2). Here, there is no dispute that claimant’s RFC is ‘medium/light.’ The dispute focuses solely on claimant’s BFC, with claimant contending that her BFC is ‘heavy’ and SAIF contending that it is ‘medium.’ Claimant has the burden of proving the nature and extent of any disability resulting from the compensable injury. ORS 656.266.
“Here, the parties do not dispute the Appellate Reviewer’s finding that the highest SVP[2] claimant attained in the last five years was her at-injury job. (Ex 35-5). Thus, we find that claimant has met the SVP requirements pursuant to former OAR 436-35-300(3). Former OAR 436-35-310(4)(c). Therefore, claimant’s BFC is determined under former OAR 436-35-310(4)(a), which provides for determination of a worker’s BFC using:
*17“‘The highest strength category assigned in the DOT [Dictionary of Occupational Titles] for the most physically demanding job that the worker has successfully performed in the five (5) years prior to determination. When a combination of DOT codes most accurately describes a worker’s duties, the highest strength for the combination of the codes shall apply.’
“The parties do not dispute that the most physically demanding job claimant performed in the five years prior to determination is her at-injury job as a CNA. The dispute arises over whether the duties of claimant’s at-injury job more closely fit within the DOT description of a nurse’s assistant (DOT 355.674-014) or an orderly (DOT 355.674-018). * * * After reviewing the record, including claimant’s testimony, we find that a combination of the two DOT codes for nurse’s assistant and orderly most accurately describes claimant’s at-injury CNA job.” (Footnote omitted.)
The Board appears to have reasoned under OAR 436-35-3103 as follows: It found that claimant satisfied the SVP requirements for her job at the time of injury. Because of that fact, she met the requirements of OAR 436-35-300(3), and, therefore, her BFC could not be calculated by using subsection (4)(c). The Board then turned to a calculation under subsection (4)(a). Under subsection (4)(a), the Board concluded that it should combine the two DOT job descriptions to most accurately describe claimant’s job at injury. As a result, *18the Board awarded claimant additional PPD for a total of 45 percent.
SAIF seeks review of the Board’s calculation and makes two assignments of error: (1) that the Board erred in its application of OAR 436-35-310(4)(a); and (2) that the Board should have instead used OAR 436-35-310(4)(c) in calculating claimant’s BFC. Claimant contends that, under either subsection, the correct BFC is “heavy.” Our first inquiry is whether the Board’s decision to reject (4)(c) as the method for calculation is supported by substantial reason.
OAR 436-35-310(4) required the Board to use the calculation that would result in the “most current” assessment of a worker’s capacity. Subsection (4)(c) authorizes the Board to use the “job at the time of injury,” under certain circumstances. Thus, subsection (4)(c) appears to be a logical beginning point for a calculation under the rule and the circumstances of this case — claimant’s job at the time of injury is likely to be the “most current” assessment. However, subsection(4)(c) can be applied only to workers who (1) do not meet the requirements of OAR 436-35-300(3) regarding formal educational and vocational training, and (2) have not had a “second-level physical capacity evaluation performed prior to the on-the-job injury.” The Board does not explain why subsection (4)(c) is inapplicable, other than to conclude that claimant had met the SVP requirements of OAR 436-35-300(3) for her job at the time of her injury. That conclusion is based on the apparent assumptions that the appellate reviewer found claimant to have satisfied the SVP requirements for her nurse’s assistant job, that the SVP for that job was the highest possible SVP claimant could obtain, and that the parties did not dispute those findings. However, SAIF disagrees that the appellate reviewer made those predicate findings and points to the appellate reviewer’s comments that he had received no work history that would permit a determination of SVP. Moreover, the parties appear to agree that claimant’s calculation should be made under subsection (4)(c), which requires a finding that she has not satisfied the SVP requirements for her job at the time of her injury under OAR 436-35-300(3).
*19OAR 436-35-300 provided, in part:
“(3) A value for a worker’s Specific Vocational Preparation (SVP) time is allowed based on the job(s) the worker has performed during the five (5) years preceding the date of issuance.
“(a) SVP is the amount of lapsed time required by a typical worker to learn the techniques, acquire the information and develop the facility needed for average performance in a specific job-worker situation. The SVP range is from 1 (lowest) to 9 (highest) associated with each DOT code. When a combination of DOT codes most accurately describes a worker’s duties, the highest SVP shall apply if the worker has met the specific vocational preparation training time for that specific code.
“(b) The worker’s SVP value is the highest SVP of any job that the worker has met in the five years prior to the date of issuance as follows:
“(A) A worker is presumed to have met the SVP training time after completing employment with one or more employers in that job classification for the time period specified in the table in section (4) of this rule.
“(B) A worker has also met the SVP for a job after successfully completing an authorized training program, on-the-job training, vocational training or apprentice training for that job classification. College training organized around a specific vocational objective is considered specific vocational training.”
Under OAR 436-35-300(3), the worker’s SVP value is based on a five-year work history and a prescribed time period of successful completion of a particular job. For instance, the DOT provides that, for the job of certified nurse’s assistant, the proper SVP value is 4. That SVP value also requires the completion of 3 to 6 months of employment in the job.
In an effort to understand the Board’s reasoning and why it decided that claimant’s calculation could not be made under subsection (4)(c), we have examined the evidentiary record. There is no evidence of a five-year work history in the record before us. Nor is there evidence that claimant successfully performed her job at the time of injury or any other job. Moreover, the appellate reviewer made his calculation under *20subsection 4(c), finding that claimant had worked only two or three months at her job when she was injured. That time period is less than the SVP requirement for claimant’s job-at-injury. In other words, the record before the Board reveals considerable evidence that the requirements of OAR 436-35-300(3) had not been satisfied. That evidence could satisfy the first requirement of subsection (4)(c). It could be that the parties agreed to the Board’s predicate findings, or that there is evidence that supports the Board’s reasoning that claimant does not meet the requirements of subsection 4(c), but those facts are not apparent to us from the Board’s opinion.
By resorting to subsection (4)(a) without expressing in other than conclusory language why it could not use subsection (4)(c), the Board has failed to adequately explain its rationale in concluding that a calculation under that subsection is more likely to result in a proper calculation of claimant’s current BFC. If a reviewing court cannot discern an agency’s rationale, it cannot determine whether the agency has erroneously interpreted the law or whether the order is supported by substantial evidence. Portland Assn. Teachers v. Mult. Sch. Dist. No. 1, 171 Or App 616, 636-37, 16 P3d 1189 (2000). We are left to “read between the lines” of the Board’s order, and “we are not inclined to decide whether [the Board] correctly interpreted the law in this regard without first knowing how [the Board] interpreted the law.” Id. at 637. We must therefore remand for an explanation of how the facts found led to the inferences and legal conclusions on which the order is based.
Reversed and remanded for reconsideration.
Former OAR 436-35-300 (1994) and former OAR 436-35-310(1994) havebeen renumbered as OAR 436-035-0300 (1996) and OAR 436-035-0310 (1996). All future references to those rules are to the former rules.
“SVP” is an abbreviation for “specific vocational preparation” or the amount of time required by a typical worker to develop the ability to perform the job. OAR 436-35-300(3)(a).
OAR 436-35-310 provides, in part:
“(4) The worker’s Base Functional Capacity (BFC) is the most current of:
“(a) The highest strength category assigned in the DOT [which, among other things, rates occupations according to the physical demands they impose] for the most physically demanding job that the worker has successfully performed in the five (5) years prior to determination. When a combination of DOT codes most accurately describes a worker’s duties, the highest strength for the combination of codes shall apply; or
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“(c) For those workers who do not meet the requirements pursuant to OAR 436-35-300(3), and who have not had a second-level physical capacity evaluation performed prior to the on-the-job injury or disease, their prior strength shall be based on the worker’s job at the time of injury.
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“(e) The following classifications shall apply to establish BFCs: sedentary (S), light (L), medium (M), heavy (H), and very heavy (VH) as defined in section (3) of this rule.” (Emphasis added.)