how to restrict the user to input number only to a textbox?

i've tried to use masked boxes, but when i link them to the ADO control, error ocurs: unable to bind the field or data member

the problem comes from the mask property..

for example, i want to make a text box to accept weight(kg) from users, so i set the mask - 999.9

is there a simple way to do the same thing?

thanks in advance
Frank