I am attempting to measure my M15 to determine if it is "standard" sail measurements or not. I already have determined that it is a bit different than some specifications given for mast length: my mast length appears to be 19'2" (Hull 176 - 1981). My confusion lies in the "I" measurement. Some measuring guides tell me to measure from the jib halyard block down to the deck (the cabin top). Another says to measure down to the deck sheer line (as if there were no cabin). Not sure how one would get that number in an attempt to guesstimate where that sheer line would be on our 15's. Which of these is the correct "I" measurement for a sail loft when having sails made? Jeff PS - It appears that I may never run out of questions for this group. Thankful that this group is so patient and helpful. *Jeff+* Molōn labe!