Store and reuse intermediate variable

[oierpa]

I make a variant of program, it use global variable ...

Code:


<<"Ins C t A " {
":C:
:t:
:A:" {1 0} V} INPUT OBJ-> -> C t A 
<<'C* (t/100/n)/(1-(1+t/100/n)^(-n*A))' -> NUM 'R' STO
'R*A*12' ->NUM 'M' STO
R "R" -> TAG
M "M" -> TAG>>
'R' PURGE
'M' PURGE 
>>

In this way I can obtain what I need, but in this way global variables are used, a practice not recommended by many.
How I can avoid use global variables?