The PVHD was developed in the mid-1970s and manufactured in the early 1980s as a cockpit instrument to assist the pilot with being better aware of the aircraft attitude at all times.
The development of the PVHD was driven by a high incidence of military aircraft accidents due to "attitude awareness issues."
[1] The initial concept demonstration was done in Canadian military laboratories and later development was undertaken by Varian Canada in Georgetown, Ontario.
In the simplest variant, the PVHD projects a dim line of light across the full width of the cockpit instrument panel.
The PVHD helps when the real world horizon is blocked by weather or darkness, and the cockpit workload is so high that full attention cannot be given to the standard attitude instrument.
A later production version used a microprocessor to sample and process the pitch/roll gyro information and a HeNe laser as a light source for the projector.