Model railroads are often operated with a “fast clock” that runs some number of times faster than real time, in order to make travel times seem more realistic. Distances on most layouts are so short that the actual travel times between stations end up being very short. Running a clock at a faster rate increases these times to more acceptable values.

A typical fact clock ratio is somewhere around 4:1 or 6:1, as that makes a session lasting a few hours seem more like a day. But, what is the best ratio to use and why?

It is interesting to note that the actual ratio used has no real bearing on the operating session and when things happen, so long as the clock speed and the printed times in a timetable share the same rate. If it takes one real hour to switch a yard, then it does not matter if the stated time is four hours at 4:1 or six hours at 6:1, the work will still take a person one real hour to complete.

So, let’s examine some examples and how they relate between real minutes and scale minutes.

At 4:1, one real minute is four scale minutes, two becomes eight, and so on, with the scale minutes being in multiples of four minutes, e.g. 4, 8, 12, 16, 20, 24, 28, and so on. If we do the same for 6:1, we get 6, 12, 18, 24, 30, 36, 42, 48, etc. Now if we consider than most people think in terms of 5 minute intervals, e.g. 5, 10, 15, 20, 30 minutes, the scale times produced from both 4:1 and 6:1 do not map well onto the time intervals that people are familiar with.

If on the other hand we choose a ratio of 5:1, then it maps very cleanly at 5, 10, 15, 20, 25, 30, etc.

So based on this analysis, it would seem that a fast clock ratio of 5:1 yields the cleanest times for operations.