It gets the degree for the current second/minute/hour using it's value. Since there are 360 degrees, 60 seconds in a minute, 360/60 equals 6 degrees step each second. The same for the minutes. But for the hours - it's different - 360 degrees, 24 hours in a day - 360/24 is 15 degrees step each hour
Note: If you don't see the minutes/hours arrows moving, Minutes are moving with each second and hours are moving with each minute!
