OK, thank you
The subtraction was going to be for specifying borders, "-3 pixels wide"
For the operations in the sets of 8 numbers, I suppose I could have
set tcp.anchor [10 40 20 20 0 1 0 1]
set tcp.xyz + tcp.anchor [0 10 0 0 0 0 0 0 0 ]
That way, my base definition is the first set and the second set moves it by 10 pixels.