Digital Protractor/Level Nd-81

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Part# 12-02651
MFR Model# ND-81


This Digital Protractor is a durable, highly accurate and affordable measuring tool built around a rugged frame that is used as a protractor, level and angle finder.

Very popular with aircraft builders, mechanics and woodworkers. Used for flight control surface rigging, setting propeller angle, and aircraft leveling and more.
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  • Larger display for easier reading
  • Heavy duty, foam padded storage carton
  • Full 360-degree measuring range with maximum resolution and accuracy of 0.1 degree
  • Simple 30 second calibration procedure using only the top flat edge of a table or desk
  • Alternate zero button to set zero starting point at any angle (commonly used for aileron, flap and elevator rigging)
  • Display hold button to freeze reading when measuring in tight spaces
  • Readout stays upright even when protractor is upside down
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Purchased and used to rig elevator and trim controls on a PA31-350. Worked excellent. From a DOM perspective the calibration process is simple and easily performed.

Josh W
February 2, 2018

Used digital incinometer on an experimental R&D aircraft on thrust vectoring apparatus with very accurate results. Repeatability is excellent, button layout and disply is common among other digital protractors as well. Only down side is that when you cross the 90 degree and 180 degree points it is a task to keep track of whether it is at plus or minus otherwise no complaints

May 29, 2013

First time it arrives, you shall do the initial calibration. It works really fine on small aircrafts (Diamond DA42 for example).

March 13, 2013


Sonora A Verified Purchase


June 5, 2021

This product was obviously used before. It arrived repackaged in a zip-loc bag. The clear plastic face was heavily marred and scratched. There was a small nick in the body. Had it been dropped? It seems to be working, but it is hard to be confident. Does it have a shorter lifespan now? I don’t like paying full price for used products. You can do better than this.

Jeffrey P
March 17, 2021

I work in a calibration shop. This device can not be described as a level because when it is calibrated, it zeroes to the surface to which it is calibrated and does not zero to a true horizontal level unlike other devices such as the pro 360. It is accurate to within greater than half a degree, repeatable to greater than half a degree, and it went into the garbage after I threw it across the hangar.

February 3, 2023


Please note, Aircraft Spruce's personnel are not certified aircraft mechanics and can only provide general support and ideas, which should not be relied upon or implemented in lieu of consulting an A&P or other qualified technician. Aircraft Spruce assumes no responsibility or liability for any issue or problem which may arise from any repair, modification or other work done from this knowledge base. Any product eligibility information provided here is based on general application guides and we recommend always referring to your specific aircraft parts manual, the parts manufacturer or consulting with a qualified mechanic.

Q: What are the dimensions of the Digital Protractor / Level ND-81?

Approximate dimensions: 6-1/4" x 2-1/2" x 1-1/4"

Q: Does this Digital Protractor / Level ND-81 come with a calibration certificate?

No, the box only includes the unit, two batteries, and the instruction sheet. The instruction sheet does include details on how to calibrate the unit once you receive it.

Q: Will this work on the horizontal plane, for example to check rudder travel?

Unfortunately not. It will only work with the horizontal flight control surfaces (ailerons, elevator, etc).

Q: Can you tell me the manufacturer of the ND-81 digital protractor?

The manufacturer of this unit is Nav-Data.

Q: How long do they stay on, Ours times out after 5 minutes. Is there an adjustment to stay on longer?

The 5 minute shutoff is a battery saving feature and cannot be adjusted.

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