Deep Six Hydrometer

[EmilyB]

I believe the Deep Six is a float arm and is temp corrected like the Seatest. I think they just want you to clean it. My guess is FW. SW coats the inside, and this is why you rinse it after use. It is probably also so you can assure a zero reading for FW.

If you can, get a refractometer, or occasionally get your SG checked by another reefer in your area.

This is a good thread on temp correction for some of those floater things....(those are calibrated for 75 degrees F)
here