Pursuant to statutory authority under 38 U.S.C. section 1155, generally each service-connected disability arising from a single disease entity is to be rated separately, and the ratings combined in accordance with the combined ratings table contained in 38 C.F.R. section 4.25, unless otherwise provided by the Secretary. See Esteban, 6 Vet. App. 259, 261 (1994); see also 38 U.S.C. § 1157 (providing the Secretary authority to "provide for combined ratings"). The purpose of the combined ratings is precisely to assess the efficiency of the individual as affected by several disabling conditions. See 38 C.F.R. § 4.25 ("Table I, Combined Ratings Table, results from the consideration of the efficiency of the individual as affected first by the most disabling condition, then by the less disabling condition"). Roper v. Nicholson, 20 Vet. App. 173, 179 (2006) aff'd, 240 F. App'x 422 (Fed. Cir. 2007).
The Secretary has prescribed a table for combined ratings in 38 C.F.R. section 4.25. The Court lacks jurisdiction to review that schedule as adopted by the Secretary. See 38 U.S.C. §§ 1155, 7252(b). Pursuant to section 4.25, combined disability ratings are calculated by adding the highest disability rating to an adjusted rating for the less severe disability. This adjusted value is computed by first subtracting the highest disability rating from 100%. The value of the lower disability rating, as determined by the RO, is then expressed as a percentage of the remainder after completing the computation just described. The combined value of the highest disability rating and the adjusted rating will then be converted to the nearest number divisible by ten. 38 C.F.R. § 4.25; Tumaning v. Brown, 4 Vet. App. 160, 161 (1993).