Has anyone tried measuring the number of drops in 1 ml of different liquids? The pg I am using measures nearly 38 drops per ml, whereas vg measures 24 drops and water 23 drops. I am using identical droppers. The pg count seems way out, and I am thinking something might be wrong. It's a mail order pg from an animal supply store somewhere in the midwest. Anyone with ideas what might be wrong, or is this normal?