If I take off and fly at low altitude my altimeter reads the wrong altitude


Most likely your flight profile doesn’t look like a typical skydive and you altimeter is autozeroing – the following article explains how autozero works.


Let’s start with some basics:

–          Atmospheric pressure reduces as you go up in altitude. The pressure at 18,000’ is about half of the pressure at sea level.

–          Skydiving altimeters do NOT measure altitude, they measure atmospheric pressure and then convert the pressure reading to the normal altitude for that pressure.

–          The atmospheric pressure at any location is constantly changing, the changes are caused by weather and atmospheric effects.

–          Your altimeter cannot “see” what is going on, it only knows if the pressure is going up or down.

When you are on the DZ your altimeter is continually measuring the slowly changing air pressure and saying, “I think we are on the ground, so the pressure I am sensing equals zero feet AGL (Above Ground Level)”, i.e. it is constantly zeroing the altitude – “Auto Zero”

When your altimeter detects a rapid reduction in pressure (which means an increase in altitude) it will say “ok, something just happened, it will remember the last time it was sure that it was on the ground and then wait for more information.

Let’s assume your altimeter detected a 500’ increase in altitude, you could be in a car, or you could be in a plane.

–          If you are in a car (maybe headed to the DZ), once you arrive at the DZ and your altitude remains somewhat constant, your altimeter needs to quickly decide that this is not a skydive and zero your altitude before you make a jump.

–          Conversely, if you are in an aircraft and you take off and then level out at 500’ for some reason, you definitely don’t want your altimeter to zero.

Your altimeter is programmed with an algorithm to decide when to auto zero.


Once a possible take off is detected, Altimaster altimeters use altitude and rate of climb to calculate a period of time before it should Auto Zero.

If you climb slowly to 500’ and then level off then it will autozero after about 10 minutes (depending on specific altitude and climb rate). Climbing to 500’ and then leveling off looks much more like a car ride than a skydive.

If you are fortunate enough to be in a fast climbing aircraft to 12,000’, it will be several hours before your altimeter auto zero’s.


Don’t worry about it, your altimeter will perform exactly as you expect.


If you are starting a skydive that is “different”, or unpredictable, for example:

–          Demo’s

–          A hold at low altitude

–          Takeoff and then descent back near to ground level

–          Long periods of time at constant altitude

You should use the “I’m on a Jump” option. After takeoff and when the altimeter has switch to the aircraft screen, select:

MENU > DZ/AC Setup > Im on a Jmp

Your altimeter now knows that this is a skydive and will not autozero.


 Your altimeter can be set in autozero mode for training purposes i.e. when you are making training jumps on the same DZ using a normal skydive profile. This is for convenience during training ONLY.

If your profile is ANYTHING other than a standard skydive profile, including:

–          Offset DZ, especially where the DZ is higher than the takeoff altitude

–          Pressurized aircraft

–          Altitude holds

You MUST program the DZ Altitude (MSL), and optionally QNH (altimeter setting) in the area of the DZ. See MA-12 user manual for detailed procedures.


The logbook on Neptune 2, N3 and Atlas all show the incorrect month and year for jumps starting with August 2017.


Please download this file: 

Download ZIP File for data bug 

to update your N3 or Atlas to fix the date bug issue.  

Important Notice

Atlas Users- You will have a prompt to put your Atlas into bootloader mode during the update. If you have trouble with the instructions provided in the update pop-ups please watch this video: 


for more instruction.

In the case you get an error message while updating you can try to delete the log on your N3/Atlas. 

Important Notice

The Neptune 2 is beyond its support period and will not be updated.

As soon the product is in our possession, either in the HQ in the USA or our European Production and Support Center in GB the turn around time is one week.

The limited warranty is 2 years after the initial sales from an authorized dealer. Please send a Proof of Purchase with your product. 

As of  January 2022 :

Galaxy US $ 90 

Atlas USB port only or pressure sensor exchange US $ 50

Atlas US$ 131 

plus shipping

Turnover time one week

In the rare cases your Atlas fails/does not charge please send it in and use this link: Repair request.


Send us a picture of the serial number and a clearly destroyed N3 and we give you a coupon code to get a 50 Dollar discount on the ATLAS. Send the Email to info@alti-2.com

Serial Number starting with:

A 2000  N 2012

B 2001   P 2013

C 2002  R 2014

D 2003  T 2015

E 2004  U 2016

F 2005  V 2017

G 2006  W 2018

H 2007  Y 2020

J 2008   2021

K 2009  2022

L 2010

M 2011

Unfortunately due to missing parts we cannot repair them any more. But you can trade them in an get a $50 discount on a new Atlas.

Yes, with one exempt : If, for whatever reason, you broke the PCB board on an Atlas produced before W175908 1/2019, we do not have these boards any more due to obsolete parts. 

The Atlas constantly self tests. When the pressure señor detects a problem the error 42 show up in the display. You need to send in the unit to exchange the sensor. If your Atlas is build after 2018, starting serial number W,X,Y,21,22 this is free of charge. All others the repair is 50 Dollar plus shipping. This also incl. updated hardware as a courtesy of Alti-2 Technologies which should give your unit another 10+ years lifetime. Please request RMA and send the unit in. The turnover time is one week.

In Europe to Alti-2 Technologies UK.

US and rest of the world :

Alti-2 Technologies Inc, in DeLand Florida

Paralog is independently sold by paralog and not a product of Alti-2 Technologies.  Please contact them for support. 

Please contact our mechanical west coast repair facility. They still have parts to help you.

RFS Robert F. Smith
GRANTS PASS, OR 97527-8764

Cell: (951) 323-1372
EMail: skytrash1@aol.com

Unlike others, we produce our altimeters in the USA (DeLand, Florida) and UK (Ipswich) in our OWN production. All our vendors are hand picked and we work with them for years. Every altimeter that leaves our production is tested. For example, every ATLAS II altimeter will go thru theses test procedures

• Charging test
• Comm connections test
• LCD test
• USB port water test
• Sub-unit front water test
• Sub-unit back water test
• Fully assembled submersion water test
• Drop test
• Backlight test
• Button functions test
• Alarm volume test
• Final dynamic profile chamber run up test with video records

Every tactical altimeters get even more testing. They go through an extreme cold test where they are quick-cooled down to -40F/C for an hour and tested thereafter.