An acute angle with the same values of trigonometric functions, up to sign, as another angle: used for easy reference when examining the non-acute angle.

plural of reference angle

(photography) Denoting or relating to a type of camera which allows the photographer to view the subject through the same lens that will be used to take a photograph, usually by incorporating a moving mirror and prism.

(photography) Abbreviation of single-lens reflex camera.

plural of reference implementation

(grammar) Abbreviation of reflexive.

plural of reflecting circle

An astronomical instrument for measuring angles, like the sextant or Hadley's quadrant, by the reflection of light from two plane mirrors which it carries, and differing from the sextant chiefly in having an entire circle.

A type of loudspeaker enclosure that uses the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies, as compared to a typical closed-box loudspeaker or an infinite baffle mounting.

A camera that permits the photographer to view the exact image that will be captured, unlike earlier viewfinder cameras.