A professional geometry triangle for technical drawings, items alignment, model making and much more you can think of.

Basic angle measurement

The application can be used when the device is flat on the table. To take a measurement, first bring the device to the start position. Press the center of the screen. The indicator will reset the angle to zero. Now bring the Phone to the target position, ideally in a steady continuous movement to improve accuracy. Read the value as indicated. You can also measure angles that are perpendicular to the table, or arbitrary, just keep in mind to rotate the Phone around its z-axis (the axis perpendicular to the device screen) to get accurate results.

Measuring angles using motion lock

When you have activated the motion lock (this is the default setting) you can perform a measurement without having to look at the display in the target position. This is especially useful when this app is used as a goniometer in a more difficult terrain. The motion lock feature is by default activated. It can be activated or deactivated in the application settings. You can adjust the sensitivity of the motion lock there too.


The in-built gyroscope accuracy varies from device to device. You can find out how your device differs from the default by taking a 180° measurement multiple times (as described in the “Basic angle measurement” paragraph) along a fixed object on your table.

Your device might indicate slightly above or below the expected 180° value. If you device shows e.g. values of 177.4, 177.8 and 177.3 then take the median value of 177.5. Now enter this value (’177.5′) into the Settings → Calibration → “180°-Turn indicates” field.

Note: Before you want to recalibrate, reset the calibration in the settings.

Further Options

✔ Rotation Mode: This controls wether the foreground triangle or the background is rotated. Set it according to your visual preference. In one case the angle digital indicator rotates with the angle, in the other mode it keeps fixed to the device. Can be switched in the toolbar or in the Settings via “Rotate Set Square” → on/off

✔ Set Square Unit Mode: Select the angle unit mode according to your preference. It can be switched via a button in the toolbar or in the settings menu “Unit Mode” that belongs to the “Set Square” group

✔ Ruler Unit Mode: You can choose inch or cm for the ruler. The ruler unit mode can be selected in the settings: “Ruler” group → “Unit Mode”

✔ Prevent Auto-Lock: If you prevent auto lock the device won’t go into power-save mode when running this application. Handle with care. By default it is switched off. Can be controlled in the Settings via “Prevent Auto-Lock”

✔ Full screen Mode: You can toggle between the full screen mode and normal screen mode via the arrow button in the toolbar.

Known Issues

The gyroscope may still drift even after a reset to zero. The drift will improve if you leave the device steady for a while.

Final notes

For recreational use only. However it CAN (!) be very accurate. The measurement is performed as good as possible (we try our best) by using the in-built gyroscope to its limits. If calibrated well the gyroscope typically is as good as 0.1° per 90° rotation.

3 thoughts on “iSetSquare

  1. Kensuke Nakajima

    I love iSetSquare very much!

    The reason is that it measures only the rotation around the line normal to the iPad display.
    It does not sense the rotation around the edge of the iPad.
    I love this feature very much, as this is the true definition of the rotation vector.
    For example, it is very useful for explaining how the sin-of-latitude factor arises in the Coriolis parameter to students in classroom.

    So, PLEASE DO NOT CHANGE this specification.
    Yours is the only app that give the rotation angle in the TRUE definition.

    Reply ?
    1. Charles Langrall

      I had been using iSetSquare with good results on my iPhone 4.

      After upgrading to iPhone 5s, the app is unfortunately completely unreliable.

      It drifts by 1 -2 degrees when measuring angles on a completely flat surface. It drifts dramatically (5 or 10 degrees or more) if not kept absolutely level when measuring angles. Have you tested the app on iPhone 5s?

      It’s a pity, I really depend on iSetSquare in my work in film to measure camera angles within +- 1 degree.

      Reply ?
      1. pb@plaincode.com Post author

        Hi Charles, this really seems to be an issue with the iPhone 5S. It is probably the same reason why the built in level (which uses the gyroscope too) doesn’t work as well on an iPhone 5S (See http://www.macrumors.com/2013/10/16/new-accelerometer-supplier-could-be-causing-incorrect-iphone-5s-level-and-compass-measurements/). I guess apple will need to fix this, and it might be a reason to change the device at an apple store, once they fixed the hardware.

        Reply ?

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