Calibration is required in odometry to reduce navigational errors. The main parameter needed to calibrate this is the measure of Distance per encoder ticks of the wheels. It is the distance traversed by the robot wheel after during each encoder tick.

The wheel base is the distance between the two differential drive wheels. Distance per encoder ticks is the distance traversed by the wheel on each encoder count. We can calibrate the robot by monitoring encoder counts of each wheel by driving for a fixed distance. The average of these counts is divided by the total distance traveled to get a starting value for the encoder click, which happens per millimeter. The encoder manufacturer may mention an encoder count in one revolution, but in a practical scenario, there will be changes in it.

To calibrate the robot, drive the robot for a fixed distance and note down the encoder counts in the left and right motor. The following equation can give an average count per millimeter...