New image transfer techniques at the end of the 19th century gave yield to innovative and practical dial designs such as the “Rate Dial” designed to Indicate Speed of Travel.
This “Rate Dial” approximates the speed of travel using the mile marker posts along the railroad track. For example, if six minutes lapses between two mile marker posts, the speed of the train is approximated at 10 miles per hour. Similarly, if only one minute passes between posts, the rate of travel is approximately 60 miles per hour.
CREDIT: PocketWatchDataBase.com