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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.


  • 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


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


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.

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