It is a method to know the underwater position by using diving equipment such as a compass.

●Water depth and temperature

When the terrain is not complicated, the shallower the water depth is the closer to the shore.
Also, the depth becomes deeper as you head offshore. Check the depth with a depth gauge.

The water temperature changes due to the inflow of rivers, spring water and depth change.

●Compass bearing

Use the compass to check the direction of your heading.

●Underwater travel time

If you swim at a constant speed, the distance traveled in a certain time will not change.
You can guess the distance traveled .

●Residual pressure gauge

If the water depth is constant, the amount of air used is almost proportional to the distance traveled.
Also, even if the water depth changes, if the same round-trip course, the amount of air used for the outbound and return is almost the same.
It is convenient to measure the amount of air used per unit travel distance in advance.

●Finkick number

You can guess the distance traveled.
It is convenient to measure the distance traveled by one finkick in advance.