Building a keypad with a slight difference

I've built a keypad and it works as you'd expect. Click on a number and and the number will appear on screen. 

However, the screen doesn't work like that. The keypad is to determine a weight and initially displays 0.000.  you press 1 it starts as 0.001, then clicked 0(or any other number, 0.010, then 0.100, then 1.000

Does anyone have any suggestion about how i could re-create this in SL?

Keypad

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