everyone seems to agree that Channel 2 was running within a minute or two of "real" time that day.
“Everyone” most certainly does not agree with this. Where did you get that idea?
In this case, we're talking about people running around with a cheap mechanical clock on their wrist that was last synchronized God knows when with a reference that was God knows haw far off of standard time.
We’re also talking about cheap manual dispatcher clocks that were last synchronized God knows when with a reference that was God knows haw far off of standard time. The difference being that there is nothing else that corroborates the time surrounding Tippit’s death with the dictabelt time checks.
That's someone who's used to missing her bus and knew to give herself more than enough time for the next one. That's not someone who I'd expect to have a good grasp of exactly what time it was.
Pure speculation. There’s no reason to believe that Markham was “used to missing her bus”..
There is one other source for time in the Tippit case that you don't realize exists. The records of Dudley Hughes Funeral Home. Back in '64, George and Patricia Nash interviewed the folks at that establishment and were allowed access to the Hughes ambulance dispatch documentation for the Tippit case. The Dudley Hughes dispatcher received the call from the DPD to dispatch an ambulance to 501 E 10th (ie, responding to Mrs Wright's call) at 1:18PM.
Then let’s see this documentation.
The "alternative" clock that I always remember offhand is in the McIntire photo of the Presidential limousine catching up to the lead car just west of the triple overpass. In the background, you can see that the Hertz clock atop the roof of the TSBD is showing "12:30."
That’s great, except we don’t know when the Hertz clock was last calibrated either and with what source. And that doesn’t help us establish timing surrounding the channel 1 dispatcher’s time checks near the time of the Tippit shooting anyway.