Diffraction and interference - why measure 10 fringes

Hi can someone please help me out on this...
if someone is conducting a double slit experiment and on the screen it forms interference fringe patterns, why would we calculate 10 fringes instead of one fringe in our calculations? I would really appreciate an explanation of this, thanks in advance

This is to get a better measurement. Because if you think about an example like measuring the thickness of a sheet of paper, to measure one sheet of paper, it'd be very difficult to get and good measurement using a ruler because the sheet is so small, so you'd have to do a lot of guessing, and therefore your value is likely to be wrong by quite a bit. However if you were to measure 100 sheets of paper, you could get a much more precise measurement, and then you could divide this by 100 to get the thickness of one sheet, which will also be more precise. So you can do the same here, measure the width of 10 fringes, then divide by 10 to get the width of one. You can also divide the uncertainty by 10 so the measurement will be more accurate!

If measuringing something small, but it repeats uniformly, measure several in one go to get a better average. The peaks may be harder to distinguish - how do you know you are right in the middle of a peak or just off? You reduce the errors by measuring across as many as you can see. If you are sure you can see 13, do that instead.

Just bear in mind that if you had 10 fringes its 9 gaps, Divide by 9.

If you use water for the slit experiment , and drop a pebble to make the wave, you can see that waves can cancel each other out and the water is higher at the noncanceled bits, use die in the water of film for closer look.

Hope this helps! :)