What is the minimum product weight and its corresponding format in excel (CSV import)?

Question

I am currently assembling a massive database.

Here are my questions,

1. What is the minimum recognized weight that a product can weigh in Magento?

   for example we have items that weight 2 grams. So if say the minimum weight in Magento was 10 grams than if someone purchased 100 of them the shipping would be very inaccurate.

2. Is there a way to denote different weight types such as some products being weighed in grams and others in pounds? Or is it say all in pounds and if an item weighs 2 grams I have to do it as a decimal? I am referring to the CSV import sheet of course regarding the proper format to import some 9000 items.