That would be a pedometer.
The word is "pedometer." A pedometer is a device that measures the distance a person walks by counting the steps taken.
foot
That is not a word, but pedometer is an instrument that measures how far a person has walked, or are you thinking of podiatry?
A measuring wheel, string or measuring tape. A laser is also used to measure distances to as far away as the moon.
The word for how far something travels is distance.
There is no instrument as far as I know
The distance
The speed of a wave is measured by calculating the distance a wave travels per unit time. It is usually expressed in meters per second (m/s) or other similar units depending on the type of wave being measured.
Light travels an infinite distance until it is absorbed by an object.
The speed of a wave is how far the wave travels in one unit of time.
Far, our, the, his, her,
Your answer depends on where you start.