I have got my Garmin out on the decking in the garden and its reading 50.1 that does seem extreme, how accurate are theses things?

is it in direct sunlight?

yes

Is it lying on a hot table or brickwork, etc? It could be reading the heat radiating from a nearby object or surface, instead of just the air temp.

right, so If I dangle it from a tree will it tell me the real temp so to speak

right, so If I dangle it from a tree will it tell me the real temp so to speak

if it is in the shade basically yes, but then you do have the effects of wind chill taking the temp down a bit.

Mate’s Garmin 500 usually overreads by about 7-8C while riding, I’m sure if he left it sitting on a table in the hot sun it’d be even worse…

(Which makes it pretty useless in summer, I suppose!)

I thought that wind chill only applied to living (warm) things? The warm layer of air they generate next to the skin is affected by the wind, so they feel colder. If you blow 20C air over a thermometer it’s still 20C air.

I’m happy to be corrected though…

I thought that wind chill only applied to living (warm) things?

moving air can remove heat from the vicinity of the thermometer (garmin) ideally you want the thermometer in a box with slatted sides in the shade, it won’t heat up, won’t be affected by air movements but air is still free to enter the box to ensure temp is correct.

moving air can remove heat from the vicinity of the thermometer (garmin) ideally you want the thermometer in a box with slatted sides in the shade, it won’t heat up, won’t be affected by air movements but air is still free to enter the box to ensure temp is correct.

I thought beej’s statement to be correct but am happy to be corrected. How can a 20C wind remove heat from a thermometer at 20C and make it read colder..? If you’re a person at 37C I can see how a 20C wind removes heat faster than still air at 20C (the same amount as, say, still air at 15C, hence feels like 15C) but if a thermometer is in equilibrium with the surrounding air – it seems that the wind should make no difference..

IIRC windchill affects wet things, effectively it’s the difference between a wet bulb temperature and dry bulb temperature.

The reason they record such low ‘windchill’ temperatures in the artic is that the air is in fact incredibly dry, in humid conditions the windchill is much lower as water isn’t evoporating, however it’s rare to get high humidity and high winds at the same time.

Temperatures are nominaly taken in the shade, it may actualy be 50C inside the garmin case, but that’s because it’s a sealed black box in the sun! Whilst riding it should be accurate due to the airflow over it reducing the effect of radiation from the sun.

Whilst riding it should be more accurate due to the airflow over it reducing the effect of radiation from the sun.

FTFY

right, so If I dangle it from a tree will it tell me the real temp so to speak

Best way to do it from a practical point of view mate

I find Garmin interfaces so frustrating that sometimes I consider dangling myself from the tree.

According to mine it was 40C when I was thrashing over Cut Gate on Sunday. Felt like it as well with the lack of breeze and after the sudden change in temperatures from a typical British Summer to heatwave overnight…

Assume this is just the temperature reported by the temperature compensation for the RF oscillator? On eTrexes, you used to have to use some key sequence to see that, but I guess they just extract it and display it thru the usual interface on newer devices.

In which case, I’d expect it to be very accurate for the purpose it was designed for, ie measuring the temperature of the device, not the temperature of the air.