Measure water of a known specific gravity (Preferably your tank's) and mark the hydrometer accordingly.
A buddy or LFS with a refractometer can measure any sample or they sell so-called reference standard solutions and you can get one for 35 ppm salinity.
You use one fluid or the other to calibrate your swing arm.
Hope this helps!
-Matt
A buddy or LFS with a refractometer can measure any sample or they sell so-called reference standard solutions and you can get one for 35 ppm salinity.
You use one fluid or the other to calibrate your swing arm.
Hope this helps!
-Matt