The first measurement below my target.
Yes, it's necessary. My target weight range is between 106.8 and 109.2; as I've said, I want my weight to fluctuate around 108, not above it. My 5-day running average still has not reached 108, though.
Weight-maintenance experts -- see Thin For Life by Anne Fletcher and Refuse to Regain by Barbara Berkeley -- recommend setting an upper maintenance limit (Berkeley calls it the Scream Weight) a few pounds above your target; if you see that number on the scale, you must act immediately to reverse the gain.
Mark, who occasionally has to design process controls for a living, took a look at the normal variation in my weight measurements and based on his statistical analysis, suggested a whole set of triggers. I am supposed to immediately start weight loss mode if I see:
Rule 1. One scale reading above 111.6
Rule 2. Two out of three consecutive readings above 110.4
Rule 3. Four out of five consecutive readings above 109.2
Rule 4. Seven in a row above the target of 108
By the way, the rules are symmetrical. I'm also supposed to enter "weight gain" mode -- whatever THAT looks like -- if I have one scale reading below 104.4, or two out of three below 105.6, and so on. I am not too worried about this happening, but you never know. So there you go, everyone who is worried I will become anorexic. I have a plan to avoid that, just in case.