Needle moving up and down What does it mean

[jb300sel]

My 1988 300SEL. There is the meter with the numbers that range from 0 1 2 3. When it’s on idle the needle is on 3, but when I engage on R or D the needle drops to less than 2. And when I am on the highway (high acceleration) the needle will then go back to just about 3. What does this mean. I recently moved from Texas to Toronto, I am not sure if this has to do with anything. Thanks.

[iwrock]

That is the oil pressure. I think that when you are at a warm idle, it should be at about one, and when more than an 1/8 throttle is applied, you should be at 3.