A. Basic prediction of Old Faithful is dependent upon the duration of the previous eruption. During visitor center hours, geyser statistics and predictions are maintained by the naturalist staff.
People speak of the average time between eruptions.
This is misleading. Intervals can range from 45-110 minutes. Visitors can check for posted prediction times in most buildings in the Old Faithful area. This has been the historical range of its recorded height. Eruptions normally last between 1.5 to 5 minutes.