This why I love the RMS on my rEvo no rules of thumb, gestimates, educated guesses etc, after a dive I have a very good indication of my remaining scrubber time AND i can track it in real time during the dive, works so well.
A fairly comprehensive evaluation of the Revo RMS and Inspo temp sticks was done a few years ago, it was surprising how accurate they were in predicting CO2 breakthrough. The study can be downloaded at
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6526050/pdf/DHMJ-49-48.pdf
Conclusion: When operated at even shallow depth, temperature sticks provided timely warning of significant CO2 breakthrough in the scenarios examined. They are much less accurate during simulated exercise at surface pressure.
The rEvo warned conservatively in all five tests (approximately 60 minutes prior). Inspiration warnings immediately preceded breakthrough in six of eight tests, but were marginally late in one test and 13 minutes late in another.