We'll be there d'reckly!The length unit of “a league” was based on the distance that a person could walk in an hour. This was eventually standardised to be 3 (English) miles.
Cornwall had its own distance units: a Cornish mile was 1½ English miles, which perhaps explains why arrival was always "d'reckly".
How fast do people normally walk?On the flat, 3 miles/hour is a pretty typical walking speed, although on “proper” Cornish terrain, it’s likely to be closer to 2. When I’m testing walks, I usually average around 2-2½ miles per hour which includes a little bit of time spent taking photos and figuring out how best to describe the directions.
Getting tired...Where possible, the iWalk Cornwall walks are designed so that the most demanding terrain is in the first half of the walk whilst you're bright-eyed and bushy-tailed and the return route is on easier terrain as you start to tire. This also has the effect of smoothing out the average speed.
Tailored to you (and picnics)Even for a given terrain, the average speed varies quite a lot between people; when my enduring parents are being dragged along, the average speed on the same walk is quite different from when I'm alone. The weather also makes quite a difference: mud or blazing heat can slow things down.
That’s why in the app, we measure your personal average speed over the last few minutes (to represent the “current terrain”) and estimate time based on this.
This also includes "picnic detection" i.e. the projection is based on when you’re actually walking, rather than stopping for lunch or a paddle. The result is that the time estimate is tailored to your individual walking pace.