I'm going to try ilfochrome printing for the first time tomorrow. I'll be printing 4x5 Velvia onto 8x10 paper, using fresh P30 chemistry and fresh paper. I have access to a colour enlarger head and a Jobo processor. I've been thinking I can get a feel for contrast and exposure times by contact printing 4 negatives onto a sheet. Due to the costs involved I'd like to get it right first time and be able to translate those numbers into numbers I can use for a real enlargement. I don't know much about printing, but I'm reasonably good with maths and physics. Presumably the inverse square law comes into effect here and I simply need to adjust my exposure times to the square of the factor of which I move the enlarger head? Does a 10 second exposure at 20cm becomes a 40 second exposure at 40cm? Any other hints/tips? I've done a bit of B&W work before, so I roughly know my way around. Unfortunately, I don't personally know anyone who prints colour so I will need to teach myself from books and forums.