If we calibrate with 3 or 4 points will there be an improvement in accuracy?

Typically, setting the zero position (the position which absolute measurements will use as a datum) after IncOder installation is usually good practice. However, calibrating with such a low number of points will only have any significant effect in very small ranges of <10degrees. Any improvement in accuracy over scales of >10degrees will require more points. This is because the error plot from an IncOder is not a smoothly varying error curve. It contains higher harmonic errors due to the way in which the IncOder’s sensors are arranged. For a calibration to have any significant effect over 360dgrees would typically require >50 calibration points. Provided the reference device is of very high quality (e.g. <10 arc-second accuracy), then the higher the number of points, the greater the effect of in-situ calibration.