Math hours, minutes and seconds can be written in colons.

For example, 3 hours, 24 minutes and 42 seconds can be written as 3: 24: 42.

Angle relation of each pointer of the clock:

(1) An ordinary clock is equivalent to a circle, and its hour hand or minute hand is equivalent to walking 360 degrees.

(2) The angle of each large grid on the clock is 30.

(3) The angle of the hour hand every 1 min should be 0.5.

(4) The angle of minute hand per 1 min should be: 6.

Stopwatches are mainly mechanical and electronic, and electronic watches can be divided into three-key and four-key categories. Physical education teachers mostly use electronic stopwatches, and mechanical stopwatches have become history in many places.

Electronic stopwatch is an advanced electronic timer. Domestic electronic seconds generally use the oscillation frequency of the synchronous oscillator as the time reference, and use 6-bit liquid crystal digital display time, which has the advantages of intuitive display, convenient reading and diverse functions.