Turn a tank a specific number of degrees
The math you're suggesting may work for going straight forward or backward where slipping is limited.  For a turn, it will not come close.  Even getting the center of rotation of the turning robot will be difficult.  The tracks will have to slip.  A tracked robot can not turn without those tracks slipping.  Differences in friction will alter the turn. More weight on the left or right, front or back of the robot will alter the turn.

Even abandoning the tracks for wheels is not guarantee that the math of how much the robot should turn will match reality.  This is not to say abandon the math, just a hint that it will only give an approximation.