I like to tell you how I became more familiar with % function of the HP12c.

VAT = Value Added Tax (in the European Union)

NET = GROSS/(1+(VAT RATE/100))

VAT = NET*(VAT RATE/100)

I wanted to write a short program which a) calculates NET amount into Y register and b) calculates VAT into X register. In this case VAT RATE is stored in R0-register. Usage: Key in the GROSS amount and press [R/S].

First I wrote the following program (16 steps)

01 RCL 0

02 1

03 0

04 0

05 /

06 1

07 +

08 /

09 ENTER

10 ENTER

11 RCL 0

12 1

13 0

14 0

15 /

16 *

Then I realized my calculator has a % function and I wrote my program again (now 7 steps)

01 1

02 RCL 0

03 %

04 +

05 /

06 RCL 0

07 %

The % function of the RPN-calculators is more useful function than I believed!