Originally Posted by Yorkshiretea
Here you go.
I am sceptical as this is a kind of advertising blurb
The erector tube also serves as the interface between the reticle and the adjustment knobs. It is here that the spindles and springs that lead back to the knobs make contact, and it is the erector tube that moves when you make your adjustments. Looking through the scope while adjusting the windage or elevation can be surprising to people. The reticle seems to move in the wrong direction. This happens because the image that arrives at the erector is actually upside down. When less elevation is dialed in the front of the erector tube is pushed down (compressing the erector spring) while the back pivots upwards, the reticle appears higher on the target. The barrel must be tilted downward to reacquire the target; this is where the reduction in elevation comes from. The exact opposite occurs when more elevation is dialed in. Windage works in a similar way, only in the horizontal rather than vertical plane. It is important to have a properly functioning erector spring to get the full range of adjustment. A cheap or worn spring can limit function at the upper end of travel.
So another view taken from the Internet.