Thanks for this information. Did the trains that stopped at hemel mainly terminate at Tring?
The short answer is no! Only a few terminated at Tring.
In the 1964 timetable (the 1956 was quite similar), the northbound trains Mo-Fr were:
6.5am Watford Junc-Bletchley (HH 6.20am)
7.5am Euston-Tring (HH 7.49am)
7.25am Euston-Rugby (HH 8.14am)
9am Euston-Bletchley (HH 9.45am)
11*53am Euston-Rugby (HH 12.37pm)
1*43pm Euston-Bletchley (HH 2.23pm)
3.33pm Watford Junc-Bletchley (HH 3.49pm)
4.21pm Euston-Bletchley (HH 5.7pm)
4.55pm Euston-Bletchley (HH 5.36pm)
5.6pm Euston-Tring (HH 5.51pm)
5.25pm Euston-Northampton (HH 6.9pm)
5.21pm Broad St-Tring (HH 6.16pm)
5.43pm Euston-Bletchley (HH 6.29pm)
6.6pm Euston-Northampton (HH 6.40pm)
6.5pm Broad St-Tring (HH 7.6pm)
6*38pm Euston-Bletchley (HH 7.19pm)
7*15pm Euston-Northampton (HH 7.57pm)
8.1pm Euston-Tring (HH 8.45pm)
9*1pm Euston-Bletchley (HH 9.43pm)
10.7pm Euston-Bletchley (HH 11.1pm)
11.10pm Euston-Bletchley (HH 11.51pm)
11*56pm Euston-Bletchley (HH 12.40am)
For completeness, although not stopping at HH, there was a 6.12pm Euston-Bletchley, stopping at Bushey, Watford, KL, Apsley, fast to Tring then all stns.
Trains marked * ran fast from Euston to Watford Junc, the others stopping also at Harrow and/or Bushey. The 6.6pm from Euston ran fast from Euston to HH, clearly the premier commuter train!, and didn't call at Tring . North of Watford all trains stopped at all stations, except the last train to call at Cheddington was the 7.15pm from Euston. The evening 'rush' service was quite respectable, but the daytime service marked by its paucity.
The service was broadly similar on Saturdays, although the afternoon 'rush' period was reduced, and the Broad St trains did not run.