[Newbies] Just playin' around

A TextMorph (string '15') and two SimpleButtons, one with a '+' and the other with a '-'.

Target for both buttons is the TextMorph. The following, executed (with DoIt) in the bottom subwindow of the '+' button inspector increments the TextMorph by 1.

(self target) contents: ((((self target) getNumericValue) + 1) printStringBase: 10).

However, a Viewer for the '+' button seems to have no target variable. And a script for the button rejects "button up?" and "button down?" tests with error messages.

Seems I'm trying to hook up some incompatible things. How would one hook up these three morphs, simply?