Barometer reading

[technion]

Hey guys,

I'm trying to use the barometer for the first time outside Kerbin.

I'm at a height of 22km over Duna. The wiki tells me the atmosphere is 40km+. If I "toggle display" it assures me it's at 0.04 pressure. However, attempting to take a reading still says "Atmospheric pressure scan can't be done right now". That's what I see when you're in a vacuum. What's required to make this work?

Edited December 21, 2013 by technion

[Geschosskopf]

Usually, you have to be at considerably less than orbital velocity. How fast are you going?

[Vanamonde]

I think it's not so much the speed as the altitude. Although you can get it to display a reading very high up, it doesn't collect meaningful science until you get into the second color-band on the atmosphere gauge. (Or somewhere around there.)

[technion]

Both your answers make similar points, I was high up and fast. I'll come down for the next try.

[thereaverofdarkness]

The barometer is much less sensitive than the atmosphere gauge on the HUD. It makes sense really, when you realize that the gauge on the HUD is probably measuring the force/resistance of air hitting the front of the ship at high speed (or we can pretend that's the case for roleplay purposes), while the barometer is measuring the net external pressure which is about the same moving fast or sitting still.