NavList:

John Howard you wrote: What I was saying was that MPP is not a dangerous misnomer but Old Fashion.  Without looking at a GPS how would you know if you were within one or two miles or even 10 to 20 miles?

John

That’s exactly what I was saying.  Your MPP might be more probable than anywhere else, but because the spread of possibilities can be high, the chances of being within a couple of miles of your MPP can be low, so you mustn’t place too much confidence in it.  We were using MPPs in the Vulcan Force into the 80s, so it’s not that old fashioned. On limited navigation exercises, with all the nav gear turned off for two or three hours flying at M0.84 above 40,000’ relying just upon celestial and a mechanical track plot, when we eventually turned on the radar and took a fix, the error was usually in the order of 3-5nm.  Occasionally it was less that 3nm and errors significantly greater than 5nm were not unknown. 
Re sailing, I’m afraid I like the smell and feel of paper charts too much to invest in a chart plotter, but I have to say that I slid into almost 100% use of my twin Garmin GPS12s far too easily except for Pilotage.  I still plot my GPS position hourly on my chart (or I did the last time I went offshore) and record course and GPS speed over the ground in my log just in case I need to start a DR plot, but I don’t recall ever having needed to.  DaveP