Some other states do not have an «exact speed limit» and drivers are responsible for maintaining a posted minimum speed (where applicable) and not exceeding a posted maximum speed. (law.stackexchange.com)
But I have to say, it is one of the most exacting speed controls in the business. (automobilemag.com)
The Mazda seemed comfortable going a couple mph faster (closer to 40 mph) than the Subaru (high 30s), but there wasn't enough time to measure exact speed differences. (extremetech.com)