At the electrical utility where I work we have digital field standards for instrument calibration. These field standards are calibrated three times a year by a "master" standard that is sent from the corporate lab. The master standard is then checked annually against some other source at the lab, which makes me wonder what that other source is trued up against.

What was the master standard that RR timepieces were checked against, and what in turn was that standard checked with?

Once they adopted "Standard Time" the signal came by telegraph from the Naval Observatory and it went all across the country via Western Union lines. Each day the Railroad Station Regulator such as you see below this post was synchronized and that would be recognized as a reliable source. Eventually slave clocks in Western Union Offices were sent the signal directly. Once radio was established they transmitted a constant "beep" signal second-by-second with tone every minute. Today, we have the atomic clock signals available.

Here is a IHC185 Find-Or-Search for "Telegraph Observatory" which contains more details.

And a link to: Timekeeping at the U.S. Naval Observatory with a lot of history.




Railroad Station Regulators were synchronized daily...

The more closely watches in railroad service were synchronized, the less time-space was required between trains for safe operation. When developing schedules, how much margin of safety was required? In other words, what was considered the minimum safe time interval between trains?

A little bit of visual explanation on how standard clocks were synchronized is here.

Christopher, typically speaking an inferior train had to clear a superior train's time by five minutes. So if train Number 16 was shown in the employee timetable as passing station X at 10:15am, any inferior train at station X must be clear of the main track by 10:10am.

I had to double check my memory with my old Uniform Code Of Operating Rules, dated 06/02 1968, which states outside ABS territory (dark territory) train order operators must block trains no less than 10 minutes apart.