rMS is simpler than that. Which, apparently, also makes it more robust. @Dr Simon Mitchell has posted somewhat recently to say that he was part of some recent research that concluded, in part, that the rEvo rMS is fairly good at serving its intended purpose. (I hope I have not misspoken too badly in my "summary") The system does not monitor breathing rate or other personal factors. But, it does accommodate them by virtue of adapting to different rates of consumption of the sorb. I.e. if you are working hard, you'll probably be breathing faster and producing more CO2. rMS doesn't know you're working hard or breathing faster. But, it will know that you are burning through your sorb faster and reflect that in the "remaining time" that is displayed on the controller.
A rEvo has 2 scrubber baskets. If it has rMS then each basket has a temperature probe in it. The probe goes right through the center of the basket and is aligned with the direction of gas flow.
I.e. when the diver is in normal horizontal trim, the probes are oriented vertically. Gas flows from the exhale counterlung underneath basket 1 (closer to the diver's head), up through it, across into the top of basket 2, and down into the inhale counterlung.
Each probe has 4 or 5 arms (I can't remember and too lazy to go down and look) sticking out at 90 degrees, at different heights. This allows the controller to measure the temperature inside the scrubber basket at different heights within the basket.
The sorb does most of its work when the gas first hits it. It gets warm as it works. So, at the start of a dive with all new sorb, the bottom of basket 1 will get warm, because that is where the "reaction front" is (where the majority of CO2 is being scrubbed out of the breathing gas). As the dive progresses, the sorb at the bottom of basket 1 will be "used up" and the reaction front will get higher and higher in basket 1 until eventually CO2 will be getting through basket 1 unscrubbed. Then, the top of basket 2 will start to scrub out CO2 and the reaction front will start to progress from the top of basket 2 towards the bottom of basket 2.
The rMS temperature probes allow the controller to tell where, in the scrubber baskets, the reaction front is. That is the basic information that it uses to estimate how much longer the sorb will last. I believe there is more to it (e.g. ambient pressure, ambient temperature, etc. - not really sure what all is factored into the calculation), but in practical terms for the diver, that is all that I think one really needs to know.
I thought it was available in both indicating and non-indicating form. It's just that nobody really cares, for CCR use, so suppliers to the dive industry generally only carry non-indicating. No CCR diver (in their right mind) is going to use sorb color as part of any decision on re-packing their scrubber or not.
