The instrument commonly used to measure distance is called a "ruler" or a "tape measure" for relatively short distances. However, for longer distances or more precise measurements, there are different instruments available depending on the context. Here are a few examples:
Rangefinder: A device that uses laser or ultrasound technology to measure the distance between the device and a target object. Rangefinders are commonly used in surveying, construction, and golf.
Odometer: A device found in vehicles that measures the distance traveled by counting the number of rotations of the vehicle's wheels.
Total Station: A surveying instrument that combines a theodolite (an optical instrument for measuring angles) and a distance measuring device (usually an EDM - Electronic Distance Measurement) to determine both angles and distances to various points on the ground.
GPS (Global Positioning System): While primarily used for determining precise location coordinates, GPS can also provide distance measurements between points by calculating the distance between the GPS receiver's current location and a target location.
These are just a few examples of instruments used to measure distance, and there are many more specialized tools and techniques available depending on the specific needs and requirements of the measurement task.