Wow, the Blichmann sight glass is one of the nicest in the industry. All glass interior with sturdy external protection. Pre-calibrated too! Oh wait a minute... dang, you can't even read the calibration markings because they were engraved with the intensity of a ant fart.
This strip of 7 year outdoor vinyl has been cut in perfect calibration position for the size kettle you have. Line it up, remove the backing, squeegee into position and remove the cover mask. Done. Pick the size kettle you have in the drop down.
https://www.youtube.com/watch?v=XPKh0RJErb8
Blichmann Boilermaker G1 Brew Kettle 15 and 20 gal 
