How do you measure km?

Answer 1

There are various methods to measure 1 km:

To measure 1 km vertically measure the air pressure (using a barometer) at sea level and then go up until the measured air pressure drops so that given the temperature, the pressure is that which is expected at a height of 1 km.

To measure 1 km along the ground use a tape measure/rule shorter than 1 km to measure the km out in sections measuring the next length from the end of the previous measured length, eg if you have a 1m rule measure the 1m one thousand times.

Using a measuring wheel - surveyors use a wheel which is 1 metre round its circumference - which counts the number of revolutions: measure the required number of revolutions. (A car mileometer uses a similar system counting the number of revolutions of the drive shaft from the gearbox to the wheels and is usually set up to over estimate the speed of the vehicle - they are about 10% accurate - but note as the tyres wear down, it will over estimate slightly more as the circumference of the wheels shrinks)

To measure 1 km from a point, measure off a distance, say 10 m (the longer the better), perpendicular to the direction wanted and then measure an angle from the end of the distance based on the length of the distance measured (eg for 10m, the angle required is arc tan(1km/10m) = arc tan(1000m/10m) = arc tan(100) ≈ 89.4°