Never broken one, but I have a question. Is that paper scale anchored in any way other than it being rolled up and pressed against the inside of the glass? what's to keep it from shifting? How do I check the calibration of mine to make sure the paper hasn't moved?
If you use pure water, it should read 1.000. If not, adjust accordingly.
Oh, and I've seen this thread and thought "Glad that's not me!"; yet here I am reporting that we need to add a +1 to the running total.