It seems that in the iOS app I’m not able to create a new numeric variable with a negative value (there is no minus sign on the keyboard). Of course the variable can become negative when I perform operations with it.
If I go to the web interface on my computer, I can create a a numeric value with a negative value.
Looks like a little bug to me.
Also in the app: the keyboard shows a decimal comma (not a point). The comma is replaced with a dot after saving it. It would be nice if this is more consistent.