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freakydiver

Neptune MSL Question

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I got my new Neptune - question though. Its just sitting on my desk at home and from time to time I look at the Alti listed for MSL and MAN does it vary. This scares me. It varies quite a bit from day to day. Am I supossed to trust this alti when in freefall or canopy mode???? Has anyone else noticed this???

-- (N.DG) "If all else fails – at least try and look under control." --

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I think you'd have to contact alti-2 for any answers like that.

Assuming your pressure sensor is functioning correctly, bear in mind that what you're seeing will happen on ANY altimeter. It's just more noticable when you can see increments of 10 feet :)
Drop alti-2 an email, I'm sure they can address any concerns you may have.

Blues,
Ian
Performance Designs Factory Team

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Ok - reading the manual - it says:

"The 'MSL' value is actually "QNE" or "Pressure Alti" which means that the value will change with barometric pressure. It is normal for the MSL reading to vary as much as +-300 feet."

Makes sense - just like you said Ian. My question I guess to the makers of this alti - what does freefall alti and canopy alti work from then if this +-300 foot QNE MSL alti can vary as much as it can.........

-- (N.DG) "If all else fails – at least try and look under control." --

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what does freefall alti and canopy alti work from then if this +-300 foot QNE MSL alti can vary as much as it can.........



I believe same as a regular alti. Zero based off of takeoff setting, but I'm guessing cause I don't know the inner workings of it's software.

Alti-2 have always been very good about responding to Q's. Drop them an email (Lara), I'm sure they'll be happy to address any questions you may have.

Blues,
Ian
Performance Designs Factory Team

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That's +/- 300 feet variation from day to day, not second to second. They're saying that at a typical location, the barametric pressure will typically vary that much. With an analog altimeter, you've gotta zero it every day. It might be off by as much as +/- 300 feet from the last time it was zeroed. A 300 foot shift in pressure altitude during the day would be a good sign of some nasty weather about to hit.

I don't know why they chose to display "MSL." The number is not particularly useful, unless you want to compute density altitude. And it shouldn't really be labeled MSL since it's really pressure altitude, a completely different thing.

If you think yours is varying too much, you might want to go into demo mode and see whats happening in all the different modes... aircraft, freefall, and canopy mode. It should not say that you're doing a 2000 fpm climb when sitting on the ground. But it will occasionally show "very slow climb" when it senses a pressure change.

Dave

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when Neptune is in ground mode it is acting like a barometer and giving you an approximate value of MSL which will vary with barometric pressure, on any given day it may vary by 300'. As soon as Neptune senses a takeoff, it will lock in the last MSL reading which ensures that the AGL (above ground level) indication is accurate.



http://www.alti-2.com/Neptune_Owners_Pages/Altitude_Displays.htm
Nobody has time to listen; because they're desperately chasing the need of being heard.

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I contacted Alti-2 about that same thing over a year ago. Essentially what has been said in this thread is correct. Although the label is MSL, that is not what it is, so trying to read it as "feet" will make no sense at all.

I was told it was a pressure reading and they decided to make it available just in case anybody cares. In my opinion, it has mostly caused confusion. I quit looking at it.

LOVE MY NEPTUNE

Ed



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This is the key:

"As soon as Neptune senses a takeoff, it will lock in the last MSL reading which ensures that the AGL (above ground level) indication is accurate."

Bottom line is use your eyes above all other methods for reading alti - I always have and always will... :)

-- (N.DG) "If all else fails – at least try and look under control." --

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so trying to read it as "feet" will make no sense at all.



I wondered about that. When jumping at DeLand, I've noticed that the MSL would read something like -300. I don't really know but if I truely was -300 feet MSL here in Florida, I would probably be under water. Although, I think I would be concerned if I saw the reading change by 40 within a couple of minutes.

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The Neptune should be cool tho!!!



Cool it is!!! I have been amazed at the accuracy of this altimeter. I occasionally glance at it when low, just because it is so amazing. If it says 20 feet, it is!!! I have watched in amazement during climbout when another Neptune is in sight and the 100 foot increments click off on both at the exact same instant all the way to altitude. I have no idea how they can be that consistent!!!???

Ed



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I've seen it vary 20-40 feet in the matter of seconds. More than once. Maybe this is normal - you wouldn't "see" that type of change on an analog altimeter - the needle would barely move...


Sudden indoor pressure changes aren't unusual. It could be happening as a result of a door opening/closing, a forced-air heating system coming on, or wind or stack effect.

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LOL That's what I've been thinking this whole time... I haven't had an alti in quite awhile so it will be weird anyhow ;);) I tell all new skydivers - use your EYES as your primary alti, I think its the best skill I ever learned - its saved my ass many a time...

-- (N.DG) "If all else fails – at least try and look under control." --

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LOL That's what I've been thinking this whole time... I haven't had an alti in quite awhile so it will be weird anyhow ;);) I tell all new skydivers - use your EYES as your primary alti, I think its the best skill I ever learned - its saved my ass many a time...



sure, but are your eyes accurate to 40ft?

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Mine are I do believe... But what I meant was, for newer jumpers to use their eyes as "freefall" altimeters. You don't really have to pay attention to low altitude all that much unless you are swooping.

-- (N.DG) "If all else fails – at least try and look under control." --

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Mine are I do believe... But what I meant was, for newer jumpers to use their eyes as "freefall" altimeters. You don't really have to pay attention to low altitude all that much unless you are swooping.



I do agree with you fully on this. I'd like to be better at it before I take advantage of the great new prices for Dytters.

But short of a malfunction, the neptune is more accurate than you are in freefall, and stays that way even going to a new DZ. Under canopy I'd imagine an experienced person could be as accurate.

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