Maximum value as a number and not string

Hallo,

I calculated the maximum value of a channel. The next step is to use that value for further calculation. My problem is that i cant use that value as a number. Its just a string. I tried it with

ChnPropGet so that i got the number. But I  cant use it for calculations. Does anybody have an idea how i can solve that problem?

I attach a screenshot of my Skript. I use the german version of DIAdem 12.

Thanks for help...