Eyepiece
The eyepiece must be adjusted to zero out the lensometer for their Rx. This is done byturning the eyepiece counterclockwise to the most plus setting and then slowly turning the eyepiece clockwise towards the minus until the reticle comes into focus.

Reticle Adjustment Knob
AKA Chrome Knurled Sleeve.

Prism Compensator
Lensometers have an attached rotary prism that allows the operator to dial in 0 to 25 diopters of prism anywhere from 0 to 360 degrees. Some older model lensometers do not contain a prism compensator but do have a ledge that allows the use of auxiliary prisms usually in increments of 3, 6, and 9 prism diopters to help neutralize high amounts of the prism.

Lens Marker
The lens marker is a simple device consisting of three spring-loaded pins that dip into a water-soluble ink to mark the lens horizontally with the center pin marking the direct point being read through the lensometer. Note that the lens marker pins and ink pad can be replaced and the ink pad requires occasional re-inking.

Gimbal (Lens Holder)
The lens holder is the arm that swivels into place to hold the lens or frame stable while taking a reading. The circular piece on the end that swivels and has legs that touch the lens is referred to as a gimbal.

Eyeglass Table
The eyeglass table is used to keep a frame-mounted and the lens aligned properly for measuring the correct axis of the lens. The table often bisects a scale mounted on the lensometer body used to measure the height of the optical center.

Magnifier
Some lensometers have this optional component which allows the operator an easier view of the axis wheel by magnifying the scale.

Axis Adjustment Wheel
The axis adjustment wheel allows the operator to align the primary and secondary power meridians in the lensometer. This is done by spinning the mires inside of the lensometer body.

Filter Control
The filter control is a small knob used to apply a green filter to the lensometer lamp for a more comfortable view through the clear material while allowing this same filter to be removed for a brighter view of filtered lenses.

Inclination Control
The inclination control is used to loosen the lensometer body from the base, this allows the operator to adjust the viewing angle of the lensometer for easier viewing.