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Yes it does, actually: "per cent" means "per 100", so, divide by 100.

50% is 50/100, or 0.5 of the whole

0.004% of the sky is 0.004/100, or 0.00004 of the whole sky.

It's right. 0.004% == 0.00004

Just like 100% is equal to 1. If the image were 100% of the sky, you would divide by 1, not 100.

Yes, and 0.002 cents == $0.002.