Here is a shot of boiling hot syrup being checked with the Hydrometer to make sure it is syrup. That little red line hovering just above the liquid shows that it has the right specific gravity for the correct sugar content that proves this is indeed maple syrup. I use this a couple of times a day to check the thermometer as barometric pressure changes during the day moving the boiling point.
Here is the thermometer just over the 7 degree mark which is 7 degrees above the boiling point of water which is the correct temperature for maple syrup. This right when I would start to draw off the syrup and would continue until it drops back down to just below the 7. Using this and the hydrometer is the best system I have found to ensure each batch is just right that I have found for my operation.