The Multi-Scale base kit consists of a Rex A scale durometer, and a choice of one or more color-coded barrel adapters for B, C, D, DO, O or OO scales. Changing scales is accomplished by unscrewing one barrel and replacing it with another — no supplementary calibration or adjustments are necessary. A test block, calibrated to the selected scale, is also included. The block allows the user to perform quick, functional checks on the instrument.