in my application I capture share prices which could vary in length and could go up to 8 decimals. Now I obviously dont want the user to type in all eight decimals..

 perhaps "nnnn.nnnnnnnnnn" and let it default to zero.

The user actually wants to display only the decimals that actually applies for example;

3.658 instead if 0003.65800000 or

23.5689 instead of 0023.56890000

I could probably persuade them otherwise.