To go back to the original topic for a minute, I use 10 mile markers for a few reasons which make sense to me at least. Ten miles is ten miles on the map, always, where ten minutes is always ten minutes but it´s representation on the map varies constantly even during a flight. That means I can draw tracks and distance markers well before the flight and know that they will be relevant when I fly. I even have the chance to study the maps and look for key landmarks in the areas where I might plan speed and heading checks. If using time marks, then I can´t do any of that and I have an annoying series of calculations to do to put the markers on the map when I probably should be thinking about other things. I suppose I could put markers based on airspeed but I know these will be wrong and will give me a cumulative series of errors to balance during the flight
When the day comes and I´m zipping along I can use the distance marks, clock and whizz wheel to do GS checks, and I do see that the minute markers would do this directly but only provided the weather guessers were spot on. In the sort of aeroplanes many people fly the groundspeed errors can be a large proportion of the calculated value and my feeling is that time markers rapidly decrease in value as the difference between marks and reality becomes larger. How do I use them, keep some running correction in my head?
When my GS is not as predicted my mile markers are still miles, I can use them as the basis for GS calculations. If I have time marks, what to do? Go back and remeasure the map to get my distance? Just seems more awkward to me.
Now to the interesting part, GPS use. Ahh the full colour moving map, where, when, how fast, more information than you can poke a stick at. Wondrous modern technology or evil seductress luring real men away from the true path of navigation?
I think they are wonderful things but I don´t trust the installations to keep working all the time which means I need a backup method. My backup method of choice is the map, watch and whiz wheel. If I am going to use that then I need to keep in practice because unless I´m in practice the workload is just too high. To keep in practice use steam driven navigation as my primary tool and the GPS for cross check when I´m going somewhere I have to navigate.
The ¨use the GPS and if that fails I´ll whip out the map¨ school of thought seems popular and I have a couple of cautions for its adherents. The first is that if you don´t have a good grounding in navigating from a map the additional workload and unfamiliar procedures are enough to make other aspects of your airmanship deteriorate. The second is don´t underestimate the difficulty of orienting yourself to a map. If you are in the wide flat country it can be just about impossible and if you are dancing with control steps then the time taken and the distraction from other things can be critical. At the very least keep a map out and keep yourself located on it.
Other people use a second (3rd, 4th) GPS and that´s probably OK provided you keep all the map packs up to date, after all you are going to be relying on it for that too, make sure they have independent power etc etc.
I choose steam driven navigation because it is not hard to do and I find a certain satisfaction in having things turn up over the nose at the appointed time using such simple tools.
Cheers, Selwyn