Abstract: At the present the joining of inductosyn scales as a coordinate measuring component on the most heavy machine tool is calibrated by doubleslides. Comparing with joining method by precision scale and reading microscope, the joining lenghth is not limited and it needn't any joining instrument. Comparing with the calibration of using laser comperater, the datum is not so sensitive to environment as laser. The error of the coordinate measuring component joined by double-slides may be estinated by the formula 1). The error n. δ is not controllable at the same time. Essencially, the distance of an electric axis of two slides (L) is a measurement unit (or electric type span gauge). It may be used to calibrate the coordinate scale, thus the error n. δ may be reduced. The digital readout made in China all have I'm meter. Every graduation pointes 1,μ(pulse equivalent 0.01). So it is possible to establish digital reading relations by itself. The relation between the point of jum meter (lm1 , ym2) and the can be computed by the formula 2). The self-calibration value (Es) can be computed by formula 3-5). Generaly, in heavy machine tools the calibration-span s>100, the double-slides is quite suitable; in plain machine tool, Os = 50, the three slides component is necessary to use (fig 1,2).Its circuit model has showed as fig 3. Adopting a special rack of double slides, the find "sight scale" can be fulfilled (point positioning error±1μ).Experiments show that the coordinate curves made by laser and double-slides is quite close (fig4).