Method 1: Freeze-frame a stopwatch. Limited to the precision of the stopwatch display. Also limited to the precision of the NTSC or PAL video link framerate. Also limited to the precision of the recording camera's framerate.
Method 2: Count the number of frames between a change on screen. Eliminates the stopwatch display's precision from the test. Can be done using anything, such as a clapper board or a flashing light, not just a stopwatch. But still restricted by the framerate of the NTSC or PAL video link and the framerate of the recording camera.
Method 3: Use a test pattern with a moving object, moving at a known speed, across a grid of a known size. The finer the grid and the faster-moving the object, the more precision the test will have. Measure the distance between the moving object on the primary and the FPV display, and convert that back to a latency number using the known speed to convert distance to time. Completely independent of any output or framerate considerations. Dependent on the physical resolution of the display, of which even a SD feed has plenty.
But here's the real question: does an HS1177 really have 50 ms of latency??? Surely not! Stay tuned...
