Yeh, thanks Larry and Bill for pointing out the obvious. Kensal's and my and Ian's point concerns a special case in which direct reading of RELATIVE constriction is accomplished quite easily without setting to say a .7 ring gauge, sleuthing out the fact of .729 or .725 or .742 main bore and then having to remove a shoe or so to deal with the real starting point when any arbitrary start will yield the same result. I like big macro hash marks for choke and for choke only. Perhaps this special case is also obvious; should be after chewing the same cabbage over and over and over. I should add that there are a host of pretty savvy guys out there who think one of those brass shoulder gauges tells all honestly. Avoiding actual measurements by the method mentioned sometimes rings a little bell for them and they get beyond the "nominal" constriction and the gauge standard bore. Mensuration is also useful for determining other info about the old sewer pipe.
jack
