It's a refractometer--aka, a pee-meter. I was looking @ the 'deals of the day' on amazon--and there it is!! I always thought they were reeaally expensive. Not really. You had to squeeze a drop of urine out of the diaper--kinda gross, but, Mary's right, you got the specific gravity.
And I do remember diy crits and other labs and "cream-o-crits" for breast milk. Then the lab realized they could generate revenue from all these things the nurses were doing for "free", and decided we weren't qualified to do any of it. Classic.
Oh, the fun you kids missed!!!