21 reversals f parallelism error e p and 2 dynamic inputs for a accumulated differential between 34 front 34 edge 40a and 34 back 34 edge 40b thickness accumulations a reversal or half turn of ring 164 occurring when accumulated thickness differential exceeds a factor of the permissible entered parallelism error e p a new differential thickness accumulation starts at each reversal of ring 164 and b sequential lamina 22 number 34 n 34 in a core 20 stack the sequential number n of laminas 22 in the stack 21 is used to determine a die ring 164 reversal when a minimum number of stack reversals q is entered so that the reversals occur at predetermined intervals in the stack 21 as will be explained and described more fully when the operator enters a number of stack 21 reversals q ______________________________________condition h______________________________________n lt n 2q 1 2 0 n 2q 1 2 lt n lt n 2q 1 2 2500 n 2q 1 2 lt n lt 1 5n 2q 1 2 0 1 5n 2q 1 2 lt n lt 1 5n 2q 1 2 2500 1 5n 2q 1 2 lt n lt 2 5n 2q 1 2 0 2 5n 2q 1 2 lt n lt 2 5n 2q 1 2 2500 2 5n 2q 1 2 lt n lt 3 5n 2q 1 2 0 3 5n 2q 1 2 lt n lt 3 5n 2q 1 2 2500 3 5n.