Rain, rain… how much rain?

Looks like we are in for some rainy weather this week.  How about a little experiment.  Place a cup outside, maybe even two and collect the rain.  How precisely can you measure it?  Many rulers have inches and centimeters on them.  If you are looking at the inches, the marks indicate different fractions. Can you find the  1/2 inch, 1/4, 1/8 and even 1/16th of an inch? With centimeters, the lines in between the centimeters are millimeters. How precise can you be?