The base is solid stainless steel with an anti-turbulence oriface to keep the liquid steady within the sight glass while there is a rolling boil in the pan it is connected to. The glass is fire polished and shatter-resistant. The scale can be placed by you to ensure the level is perfectly calibrated to your pan.
This Sight Glass configuration will still allow you to draw off syrup from this port. You will just have the added benefit of being able to see your pan’s sap level.
NOTE: Always keep your sap level at about 2″ depth to prevent scorching of your syrup and pan. If your Sight Glass indicates that you have 1″ depth, that actually means that you have 1″ OR LOWER, and you should add sap right away.