1, alas! When measuring, you can only move in the same direction, and you can't advance or retreat. If it is from right to left, you can cut the outer side of the dark ring first, but after passing through the center, you should cut it with the inner side of the dark ring in turn, because when measuring the diameter of a stripe, if the right side measures the outer position and the left side measures the inner position, the straight line of the stripe is the distance between the two positions (why let me think again, hehe).

2. It must have an impact. When measuring, the number on one side is subtracted from the number on the other side to get 2R. If you don't aim at your numbers, it's difficult to count the series. Even if the numbers are right, if you are biased, one number will definitely decrease and the other number will increase, so the measured value will be very large.

3. The refractive index in the interlayer is not between the refractive index of the lens and the glass plate. At the contact point between the convex surface of the lens and the glass, the thickness of the air layer is 0, and the optical path difference of the two reflected lights is λ/2, so the center of Newton's ring in the direction of the reflected light is a dark spot. The direction of transmitted light is opposite to the direction of reflected light stripes, so the center of Newton's ring of transmitted light is a bright spot. If the refractive index in the interlayer is just between the refractive index of the lens and the glass plate, the center of the reflected Newton ring is a bright spot, and the transmitted Newton ring is a dark spot. In order to answer this question, I took out all the physics books I learned last semester. I need to use my answer. I don't know anything, I can communicate, hehe! If you don't understand, we'll discuss it. Give me some advice.