ESDU Perf RG2/1 gives simple methods for the incremental adjustment to a desired standard or datum condition of distances and speeds measured in tests. It applies to conventional aircraft and any changes to the vertical thrust component are neglected in the reduction process. In deriving lift coefficient@ vertical acceleration and any vertical thrust component are also neglected. Corrections are given@ to be applied to the airborne phase or ground run (which itself may be divided into phases) as appropriate@ for non-standard values of wind@ runway gradient@ speeds@ thrust@ weight@ density@ and effective coefficient of friction. Two worked examples illustrate the use of the methods.