Need to ensure a product has a minimum weight

In the admin page products_insert.php I have attempted to amend the weight text box to have a minimum weight of 0.01kg, but it breaks it's link to the DB when I change it.

So I have:

<input name="ProductWeight" type="text" id="ProductWeight" onBlur="" value="<?php echo(isset($_SESSION["WAVT_ProductsInsert_Errors"])?ValidatedField("ProductsInsert","ProductWeight"):"") ?>" size="32" />

and I m trying and have tried numerous ways of trying to post 0.01 without breaking the code for the insert or validation.

I've tried adding 0.01 to the DB column as a default value if the weight text box is left empty, but the DB shows -1.00.

Any thoughts?

Thanks.