What is the shortest unit of time

What is the shortest unit of time

The shortest unit of time is picosecond, 1 picosecond = 1 * 10e - 12 seconds

A problem about measuring the diameter of thin copper wire
The method of measuring the diameter of the thin copper wire is to wind the thin copper wire tightly on the round pencil, count the number of turns n of the thin copper wire, measure the length L of the thin copper wire on the round pencil, and the diameter of the thin copper wire is LGN. But when I do a question, I count the number of turns of the thin copper wire one by one, and the number of turns is 33, But the answer is 32. At that time, I thought the answer was wrong. But later, when the teacher talked about another problem, the teacher Ms said that the number of laps should be subtracted by 1 and so on. I don't quite understand, and I can't remember what the teacher said clearly
Who can help me tell me how to count the turns of thin copper wire? With or without 1?

Your teacher said subtract 1, is it because considering the two ends of the circle is half circle, so you want to subtract 1. I suggest you count the most number of circles, and then subtract 1

Measuring the diameter of thin copper wire
The diameter of the thin copper wire is L / N when the length L of the solenoid is measured with a scale
Why is this? Is the length and number of turns of the solenoid related to the diameter of the copper wire used?

As shown in the figure, l = 2cm, n = 20 turns, copper wire diameter = L / N = 2cm / 20 = 0.1cm