The most commonly used video time inserters in the video recording for occultations of stars by the moon, and stars by asteroids, are the KIWI-OSD and the IOTA-VTI.
The KIWI-OSD in no longer available for purchase, although apparently those that have them continue to use them. They have seen about 12 years of active service. A very important point, when using these units,
"is that once started, KIWI-OSD needs to left to run for at least 15 minutes, and the Reset button pressed twice before using KIWI-OSD to time an event. Pressed once (after 15 minutes), to allow plenty of time for a current GPS almanac to be downloaded, getting either; "Previous times ok", OR "Error: use field count" messages, and pressed again to restart KIWI-OSD. Even then, it's a good idea to record the entire 2nd restart sequence and a couple of seconds of time display. Then should KIW-OSD display an unexpected "Error: use field count" message, at least you'll have some video fields with good timings that is a basis for counting fields, thereby salvaging your observation." (Dave Gault).
Dave Gault also has the following information:
Start the clock once the time display starts. The download of the current almanac should take 12.5 minutes (Max.), provided the GPS has a good signal throughout. The established practice is to make Kiwi the first thing you setup and get going. Once you have the scope going, Kiwi would have completed it's housekeeping, then simply press the reset button - twice and you should be good to go.
If one gets the "Error: use field count" message then what is the procedure to obtain accurate timings?
The procedure is to:
NTSC video runs at 59.94 fields per second. PAL runs at 50 fields per second. Simple math should give you the duration between calibration and event times.
The links below provide the user manual and the firmware upgrade.
The IOTA-VTI is the current time inserter used by occultationists. It has went through several versions. Those with serial numbers below 500 are the older models which are contained within a black housing. The new version have serial numbers above 500 and are bone in color. They can by ordered directly from the Video Timers website.
Below are listed the two operating manuals for the old and new units. The website also has additional information on the features with a FAQ.