Abstract: A method and kit are disclosed for recalibrating a factory-prepared relationship between concentration and expected signal R.sub.exp produced by an analyzer. The method and kit use two or three calibrators at the field to obtain an actual signal R.sub.act for the two calibrators C.sub.low and C.sub.high, for example, and these two actual signals are used to create a ratio of R.sub.actlow /R.sub.explow and R.sub.acthigh /R.sub.exphigh. The first of these is used to correct the expected signals for concentrations below the lower calibrator concentration, and the second is used to correct expected signals for concentrations above the higher calibrator concentration, producing pseudosignals PS.sub.low and PS.sub.high. A straight-line relationship is applied between the corrected PS.sub.low and PS.sub.high, and that relationship is used for concentrations between C.sub.low and C.sub.high.