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Digital Air Density Gauge Instructions

  • To turn gauge on push Button on right side at top. Display shows current air density and either current barometric pressure and temperature – OR – Air Density Baseline and difference. Push Button once quickly to change from one to the other. The gauge shuts off after 1 minute to save the battery. (To force shutoff push button and hold until display flashes - 3 seconds, then release button.)


  • To set your Baseline push the Button and hold it 10 seconds (display flashes after 3 seconds - continue to hold.) The display will change to show current and Baseline air density the same. After that the Baseline stays as the current air density changes. The difference, + or -, is shown on the right. When the difference is greater than 5% a red LED on the left side flashes to remind you.

Digital air density gauge display    Digital air density gauge battery indicator


Using the Air Density Gauge:

To use the Air Density Gauge open the case and place the gauge in the shade so the sun will not warm it. Leave it there for at least 30 minutes to equalize the temperature.

Next get your jetting exactly where you want it by trial and error, reading the spark plugs or using an exhaust gas temp gauge.

Record the air density or set the Baseline (see above). After that when the air density changes you can re-jet to keep your motor running its best. The amount of jet change per % change in air density varies with the motor and fuel intake system. On a Holley® carb a good rule of thumb is 1 jet size change for every 3% difference. Yours may vary somewhat. Longacre has a circular slide rule to calculate the exact jet change. See part number 50941.


Converting the auto-shutoff, pressure and temperature readings:

To convert your gauge complete the following. Pressure can only be set to hPa, mmHg, or inHg.

With the unit off push and hold the button for 3 seconds (after 1 second the regular display will come on – continue to hold). This gets you into the setup mode (display says ‘SET’. The first option is auto-off time. Push the button to cycle thru the options, from zero (- - -) to 30 minutes if you wish. If not go to the next step.

Next hold the button 3 seconds again (unit on this time). Now the barometric pressure screen flashes (lower left corner). These are very tiny. Push the button to cycle thru the 3 options.

Next hold the button again for 3 seconds (again unit still on). The temperature display will flash. Push the button once to change to C from F. At this point allow the unit to auto-shutoff.

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