2m Metric/English Folding Fiberglass Rule

We designed our own crystal card with very specific details in mind.  A card with volumes of material printed on it defeats the purpose of a crystal card – to look at snow crystals! We only have a 2 mm grid on our card. That way, no matter what camera, what magnification, and what loupe you use, you always know the crystal size. We found that 2 mm is a good compromise as it easily allows you to assess size of the smallest rounds or needles, while still sizing the biggest depth hoar and surface hoar.