Spilts/altimeter watch

[Adventure Racer]

You do get drift over time with the S710i - I'm fairly sure it's due to temperature change as it cools down from body heat due to movement through the air, as I see a consistent drift downwards at the start of a session (in theory it's supposed to be used on a handlebar mount, and I find if I haven't been wearing it and use it there I don't get the same drift). On hill intervals I find my start point drops during the session! Seems consistent once it's settled over a longer period though, so fine for contouring at the end of an event, but not the start

Your point about elite level is a given, since as you say some don't need a compass either. Different for those of us not at that level.

[candyman]

Good point on the temperature, when I have looked at that on the watch it rises consistently through the session as skin temperature increases and I bet that is what causes the drift in altitude. So if you want to cheat with an altimeter in orienteering don't wear it as a watch!

[graeme]

So, how does it work then? I assume the watch measures temperature and pressure separately (and you don't have to recalibrate either), in which case it should be able to distinguish between changes in pressure due to temperature rise and due to height rise. Or maybe there aren't independent barometers and thermometers?

[candyman]

Note: If the current air temperature differs from the normal (see the table below), there are errors in altitude calculation, because the altitude calculation is based on the barometric pressure at a normal temperature. When climbing in higher than normal temperature the actual altitude value is higher compared to the value shown at the wrist unit's display. If the temperature is lower than normal temperature the actual altitude value is lower than the value shown on the wrist unit.

From the Polar website, so I assume if your skin temperature causes the air in the altimeter in the watch to rise in temperature it will also cause the estimated altitude value to rise.

So I assume that the watch does not actually adjust its measurements based on it's temperature reading... kind of strange that it bothers to measure temperature at all?

[Adventure Racer]

Good point on the temperature, when I have looked at that on the watch it rises consistently through the session as skin temperature increases and I bet that is what causes the drift in altitude. So if you want to cheat with an altimeter in orienteering don't wear it as a watch!

Checked my most recent hill session again, and the temperature definitely drops along with the altitude during the session, so I seem to get differing results to you!

Logically you'd expect the pressure to decrease with decreasing temperature, so maybe the watch is correcting properly for temperature - it sees the temperature decreasing, but no corresponding decrease in pressure, so concludes that you've actually descended since the effective pressure has increased.

[grubby]

Don't like the sound of you doing too many of those hill sessions before the night season starts, Adventure Racer. . . . . . . . . . . . .

Different models of altimeter 'measure' the altitude a different number of times per minute. Some of the very early models only took one reading per minute.