Unfortunately, at the time, Mr Ling did. I think the volume of water aspirated in n-seconds was used to give us a clue to performance (actually this was recommended by the manufacturer). Measuring water volume and time is easy (without a flow meter) but it can be a bit messy. Otherwise it's a bit subjective trying to guess performance of anything that "sucks or blows". We use the newer LSU and have fancy flow meter(s) where I work nowadays. The older LSUs are just too unreliable in my experience; irrespective of how much suck they have on a good day and how accurately it can be measured.
