How do I increase a variable as another variable is decreased?

I want to increase a variable relative to the amount another variable is decreased. I think its called 'negative correlation'.

I realise that this his is rather a math question than C3 specific, but in my case I want to decrease a Sin period as the speed of my object increases.

Cheers

every tick add one to variable 1

variable 2 set value to - variable 1

or

every tick subtract one to variable 1

variable 2 set value to - variable 1

Something like this?