Freeze again, and repeat twice more at hourly intervals.

This has run at weekdays at hourly intervals.

Apart from the trains in the early morning and late evening, a service at hourly intervals was offered, and trains stopped at all stations.

All routes run at hourly intervals.

Other magnetic observatories were manually operated and typically only took readings at hourly intervals unless there was a magnetic storm, in which case readings were taken at 15 minute intervals.