memory map / wow!

[Alex728]

well I decided to buy a copy of Memory Map (1:50000 Central England) and not only is this impressive software, I have now been able to compare a GPS trail on my normal pushbike (a Raleigh Pioneer hybrid, 700c x 28 wheels, 21 speed) with the Powacycle Salisbury..

Until looking at this I didn't realise just how much the electric assist had increased my speed considering its a lower powered motor.. I'm happy though as I'm still getting the exercise but getting around quicker, best of both worlds for me..

one other question though... when a hill says 1 : 20 or 5% gradient, how is this actually worked out if I have a profile of the hill and how many feet it rises against the distance?

I did look here but wasn't sure which of the formulae to use (high school maths was some two decades ago..)

http://en.wikipedia.org/wiki/Grade_(slope)

 

[flecc]

Simple maths easiest Alex, just divide the rise into the distance and that gives you the "1 in X". To get the percentage rise, just divide 100 by the X number.

For example, with a rise of 380 metres in 1790 metres distance:

1790 divided by 380 = 1 in 4.7

100 divided by that 4.7 = 21%

If the distance used is that over the ground on one continuous hill rather than the map distance, the hypotenuse has been used instead of the distance over the earth's surface, which contains an inaccuracy by one interpretation. For our purposes and hills the discrepancy is tiny.

To give some idea of the size of the error, a 12% will actually be an 11.91457%, a 7% will actually be 6.98291%, so you can see why I don't think the difference is worth bothering with. Even a 20% will only vary slightly, the correct gradient being 19.611688%. Not relevant for us I think.

P.S. Your Wikipedia link isn't working.
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[Alex728]

thanks - managed to suss it out in the end (after a false start trying to compare miles with feet - d'oh!) - in my defence like most people my age I was taught mostly in metric but have by GPS and memory map set up for miles and feet so have to convert each time..

I am sure this mixing of units confuses generations of British youths when they are taught geography, as although you are taught in metric the moment you get out on the road everything is back in miles and yards or electronic kit reads in decimal fractions of a mile

 

[flecc]

Yes, I find today's young are often baffled by imperial measure.

I'm lucky since I grew up with imperial but went straight into engineering from school where I regularly used metric all my life as a matter of course, so I'm equally familiar and can convert "on the run" without thinking about it.

I've always been firmly of the opinion that imperial measure is far superior for day to day general use than the inappropriate metric units and we should not have converted, leaving metric teaching and use for scientific and engineering purposes. The USA has managed very nicely doing that and is far from being a left behind third world country. Even at this late stage I think we should reverse school teaching to imperial measure for normal day to day purposes.
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