Decimals?

Hi,
I have just installed and tried this plugin as well as your Grouped Product plugin. They would have worked great except for the fact that I was not able to set the product amount to “0.3” (or “0,3”, I tried both). Customers are able to buy our products (fabrics) in smaller amounts than 1 (meter), so this is very important. How would I achieve this with your plugin?
Thanks for your help,
Jenny