I will change the way I format the prior calculations in the future.
The point is, that Primes column- or row-selectors (ctr-shift-c, ctrl-shift-r) always return a matrix, a column resp. a row vector. Thats true even when its just a 1x1 vector/matrix.
To access the element of a vector or matrix you have to use indices, either v[i or M[i,j
Your point about units is noted – thanks.
Mathcad 15 uses SUC (static unit checking) and there is no need to assign a unit to a zero value.
Prime had done away with SUC (fortunately) and so in some circumstances it can't decide which unit to assign a zero value to and may fail. In Prime we also have to new "units", zero and Zero, to cope with problems which may arise because of this behaviour. Assigning a unit to a zero value may look unnecessary work, but sometimes its simply necessary in Prime and furthermore I think doing so may increase the readability of worksheet sometimes.