Make sure your hydrometer reads 1.000 in distilled water. If not, adjust up or down accordingly. I find it is rare to find a hydrometer that stays calibrated for long.
Absolutely agree on verifying at 60 degrees, but how might it deviate over time? There's quite little to fail, except catastrophically. The paper could shift or the weights could come loose possibly, but I didn't think these were common scenarios.