The first thing to understand is that hydrometer readings are affected by two things:
- The Sugar Density
- The Temperature of the Syrup Sample
The reason your hydrometer has two different “finishing lines” on it is due to the temperature variable. One line represents the “Cold Test” (60ºF) and the other line represents the “Hot Test” (211ºF). Both of those lines are telling you where the syrup should float if you have perfect density (66.9º BRIX). But what do you do if your syrup is any temperature other than 60ºF or 211ºF?
Before the Murphy Cup, sugar makers had to take the temperature of the syrup sample with a thermometer and then reference a compensation chart to calculate where the hydrometer should be floating if it is 66.9º BRIX. All the while, temperature of the sample could be changing, and temperature was a moving target. The Murphy Dial simplifies the process so that your regular thermometer and compensation chart are no longer needed.
The Murphy Dial displays your TARGET — or the “finishing line” — that your hydrometer must match. Use your hydrometer reading to determine if your sugar density is higher or lower than the target.
If the hydrometer and dial readings match, the syrup is perfect density (66.9º BRIX).
If the hydrometer reading is LOWER than the dial’s reading, your syrup’s sugar density is LOWER than 66.9º BRIX. Therefore, keep boiling.
If the hydrometer reading is HIGHER than the dial’s reading, your syrup’s sugar density is HIGHER than 66.9º BRIX. Slowly stir in distilled water or sap to reclaim perfect density.