We do the same thing to check out hydrometers. We have three that we check against each other. Have found that they all vary slightly. Same with digital thermometers. They all vary slightly. That is the fun part of sugaring; lots of little variables that make it challenging. You are much braver than I am Happy Thoughts, I would never attempt to make syrup without a hydrometer.
John
2 x 8 custom arch, custom raised flue pan, AOF/AUF, custom auto draw off and other automation
400 taps (buckets and tubing)
18 x 24 timber frame shack
Two daughters that are a LOT of help
Greyhound that drinks sap (and has gas)
2011 Gator 825 XUV with 100 gallon tank
5 275 gallon IBC totes for storage