If they are sitting on your shelf for a while with the battery in them sometimes the screen will freeze i.e. it will show 0.00 and no matter how you move the jaws or what buttons you push it won't work. Normally this is easy to fix in the following manner:
    a) remove the battery
    b) leave out overnight
    c) replace the battery
    d) move the jaws along the slide a few times & it will operate perfectly.