PRO 360 Digital Protractor Calibration

The PRO 360 Digital Protractor is an innovative angle measurement device that provides a digital reading of all angles in a full 360° range. The protractor contains an advanced liquid-filled angle sensor that changes its electrical properties as the angle of the protractor is changed. The variations to the electrical signal are measured by a precision microprocessor to provide a highly accurate angle measurement.

The full-scale range of the protractor is divided into four quadrants providing a 0.0 to 90.0° reading in each quadrant. The Pro 360 Protractor has an accuracy of ± 0.1° at 0° and 90° and an accuracy of ± 0.2° for all angles in between.

The sensor is housed in a lightweight, machined aluminum frame that provides a stable base for measurements on all surfaces. The frame contains a V-shaped groove along the bottom surface to use with rounded objects such as shafts or pipes. Threaded holes on the bottom can be used to attach the protractor to custom fixtures or various attachments.

Display Features

The front panel buttons contain two very useful features to make the most out of the unit. Pressing the ‘Alt Zero’ button will electronically zero the display to establish a new reference plane anywhere within the digital protractor’s 360° range. The ‘Hold’ button stores the last displayed angle on the LCD to temporarily capture a reading.

Superset Feature

The PRO 360 contains a ‘Superset’ calibration feature that is designed to easily reset its internal readings in the field to maintain the manufacturer’s accuracies. The Superset procedure is performed by placing the unit on any flat surface for the 0° reading and any vertical surface for the 90° reading to readjust the reading to those values. The protractor will be rotated and flipped during the procedure to set the values for all four quadrants.

The Superset feature should not be regarded as a true calibration of the protractor. If the Superset procedure is not performed properly, errors could be present in the protractor’s measurements. The only way to ensure that the protractor is measuring accurately is to compare the protractor’s measurement with a precision standard of a higher accuracy.

A proper calibration will also check various angles between the 0° and 90° settings of the Superset procedure to verify that the readings are linear throughout the full range of the protractor.

PRO 360 Calibration Procedure

Calibration of the protractor is accomplished by comparing the protractor’s readings at 0°, 90° and 45° at a minimum. Other specific angles can also be checked by using the procedure below.

The 0° angle is typically checked on a leveled Surface Plate. The level of the Surface Plate is checked with a Precision Bubble Level with an accuracy of less than 0.025° (90 arcsec).

The protractor needs to be rotated and flipped so that all four quadrants are checked for all readings. The display should be allowed to stabilize for 10 seconds before a reading is taken.

The 90° angle is checked by using a Granite or Cylindrical Square placed upon the Surface Plate. The 90° angle is created by the intersection of the face of the Square and the top surface of the Surface Plate.

The 45° angle, or any other angle to be checked, involves the use of a Sine Bar and Gage Blocks. A Sine Bar is a precision beam with two precision ground cylinders at each end that are at a precise length between them, typically 5 or 10 inches.

One cylinder will rest on the Surface Plate and the other cylinder is placed on top of a Gage Block stack to form a right triangle with the Sine Bar being the hypotenuse of the triangle. The specific height of the Gage Block stack is calculated through trigonometry by taking the ‘sine’ of the desired angle and multiplying that value by the length of the Sine Bar.

For example, to calculate the value for a 45° angle using a 10-inch Sine Bar, multiply the sine of 45 (0.70711) by 10 and the length of the Gage Block stack calculates to be 7.0711 inches. For 30°, the sine of 30 is 0.5 so the Gage Block stack needs to be 5.0 inches.

If any inaccuracies are found during the calibration, the Superset procedure can be performed and the measurements of the protractor checked again.

has the capability to properly calibrate your PRO 360 Digital Protractor or other similar angle measuring instruments. For more information on our full calibration capabilities, contact e2b calibration.

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