Hi - we usually use a simple respirometer, with soda lime, & coloured water in capillary tube. This used to work, but I cannot get a seal since acquiring plastic 3-way taps, even after dispensing with the darned things.....So teachers have decided to use the 'U' tubed manometers in a repeat attempt on this Core A-level prac tomorrow! The respirometer / manometer print out I have uses KOH to absorb the CO2, rather than soda lime, but fails to give any indication of solution strength. A simple prep. morning is now very stressful. Help please. Thanks, Heather ps - what's the difference between R & M? - any??