What is a primary function of a tachymeter?

A tachymeter is specifically designed to measure speed based on the distance traveled over a set period of time. This function is particularly valuable in various fields, such as racing or aviation, where quick calculations of speed are essential. The tachymetric scale typically appears on the bezel or dial of a watch and allows the wearer to calculate speed by timing how long it takes to travel a known distance.

For instance, if a user covers one kilometer in 30 seconds, the tachymeter scale would indicate the speed in kilometers per hour. This adjustment enables quick and efficient measurements without the need for complex calculations.

In contrast, other functions mentioned in the question do not align with the primary purpose of a tachymeter. Measuring distance traveled, determining altitude, or tracking the daily time of sunset are functions associated with different instruments or measurements, but not with the tachymetric capabilities of a watch. These activities might involve other features such as GPS, altimeters, or calendar functions, which are distinct from the speed measurement that a tachymeter provides.