Parts of a Lensatic Compass – Labeled Diagram and Quiz

All 13 parts on the diagram

Show the list

First 6: the main parts 6

Cover One of the three main parts. It protects the floating dial, and it carries the sighting wire and two luminous dots for use at night.
Base (case) One of the three main parts. The floating dial, the bezel ring and the thumb loop are all on it. The maker calls it the case.
Floating dial It sits on a pivot. It turns freely once the compass is level. It has two scales: the outer in mils and the inner in degrees.
North arrow (luminous magnetic arrow) It always points to magnetic north. It is luminous, so it shows in the dark.
Lens One of the three main parts. The user looks through it to read the dial while sighting.
Sighting wire It is the front sight. The user lines it up on a distant object, looking through the sighting slot.

The smaller parts 7

Bezel ring It turns with a click, and each click is 3 degrees. Turning it moves the short luminous line.
Fixed index line It does not move. The direction is read where the dial passes under it.
Short luminous line (bezel indicator) It turns with the bezel ring. Set over the north arrow, it marks a direction so a course can be kept, day or night.
Rear sight (lens bracket) Folded down, it locks the dial to protect it. It must be raised well up before the dial can float freely.
Sighting slot The user looks through it and aligns it with the sighting wire. The maker calls it the sight groove.
Thumb loop The thumb goes through it to hold the compass steady for sighting. Folded forward, it holds the compass shut.
Straight edge (scale edge) It is a scale for measuring distance on a 1:50,000 map. It is also a straight edge for drawing lines.

How this list was compiled: Part names checked on 2026-09-30, each against both of these. (1) US Army, FM 3-25.26 Map Reading and Land Navigation, section 9-2 Lensatic Compass (and the same section, 8-2, of its successor TC 3-25.26), a US government work, full text at https://archive.org/details/FM3-25x26 and https://archive.org/details/map-reading-and-land-navigation-tc-3-25-26 (cover, sighting wire, base, floating dial, arrow, fixed black index line, bezel ring, short luminous line, thumb loop, lens, rear sight and rear-sight slot, straightedge). (2) The compass maker's instructional booklet, full text at https://archive.org/details/manualzilla-id-5760574 (case cover, sight wire, case, dial and its north arrow, index line, bezel, luminous bezel indicator, lens bracket, lens, sight groove, thumb loop, scale edge). Also read: Wikipedia, Compass and Hand compass, and the US Air Force handbook AFH 10-644, section 18.16, which follows the Army text. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry, a composite of no one make; nothing traced. Licence: own work

How it works

A lensatic compass has three main parts, the cover, the base and the lens. If a worksheet asks you to label the numbered parts of the lensatic compass, these are the 13 names it wants.

Read the full guide

Read the drawing

The upper drawing is the compass opened flat, seen from above, with the cover to the left. The floating dial is in the base, under a glass with a fixed index line, inside the bezel ring. The rear sight, with the lens, folds out to the right, and the thumb loop is beyond it.

How the parts work together

The small drawing underneath shows the compass held for sighting: cover upright, rear sight leaning over the dial. The user looks through the sighting slot, lines the sighting wire up on an object, and reads the dial through the lens at the index line.

Cover, base, lens: learn the three main parts first, then the smaller parts on each.
The index line is fixed; the short luminous line turns with the bezel ring.

Questions and answers

What are the three major parts of a lensatic compass?

The cover, the base and the lens. The cover protects the dial and carries the sighting wire. The base holds the floating dial, the bezel ring and the thumb loop. The lens is for reading the dial.

What does the bezel ring on a lensatic compass do?

It turns with a click, and each click is 3 degrees. The short luminous line in its glass turns with it, and is set over the north arrow to mark a course that can be followed even in the dark.

Why is it called a lensatic compass?

Because the dial is read through a lens. The lens is in the rear sight, so the user can line up an object through the slot and the wire and read its direction at the same moment.

What is the straight edge on a lensatic compass for?

It is a ruled scale along one side of the opened compass. It measures distance on a 1:50,000 map and works as a straight edge for drawing a line on the map.