Suppose we add a constant term,c, to each of N variables, A, B, C, …, N say, and wish to compute the variable mean. We can so this in SPSS using the syntax in the box

Compute newmean  =  Mean(A,B,…,N) +  c. 

This uses the compute statement and the mean function MEAN(A,B,…N) to obtain MEAN(A+c,B+c,…..N+c). This saves time creating new variables by using the original metrics.The RHS in the above box may be, alternatively, input into the compute window under by choosing analyze:compute in the menu.

Variances are not effected by addition of a constant term.