How do I change the number of variables in a custom equation in the curve fitting tool?

So for example, on this page, we see a custom equation that only has variables x and y. But when I open the cftool, it defaults to wanting x, y, and z; and I cannot figure out how to change this. I'm sure it's something simple, but I can't find it myself and don't see it answered anywhere else.

Answer 1

[Stephan]

Hi,

if you work with only x and y just leave z out.

Best regards

Stephan

[Thomas Veith]

LOL it goes right away, I was just SURE you'd have to change it before entering your data. Thanks!

[zhou echo]

how to change it? buddy?