Hydrometer

[rayjay]

I have two that I've been using now for 20 yrs but they are Sea Test swing arms, which were the best ones when Randy Holmes Farley did the hydrometer testing.
There are things to do to help ensure accuracy though.
Always "tin" the hydrometer before using it by soaking it in water a minute or two.
Fill the hydrometer with the tank water, slowly and take the reading on the second fill.
Be sure there are no bubbles on the swing arm. Even the tiniest ones screw the reading.
Take two readings and if they differ, take another to be sure which is correct.
After testing, rinse in plain water.
Once a week, soak the hydrometer in white vinegar overnight.