Stan, Oh, that's a very important feature. I wish other cameras had considered making that available. The higher the pressure the closer the air molecules are squeezed together. The closer together they are, the harder photons have to work to get through all of them and arrive at your sensor. The harder the photons have to work the less energy it has left to affect the sensor and one gets a weak picture.

Here's an example. One goes to the mall in mid summer. The speed with which they can arrive at the store they want is relatively unimpeded. Now feature the same mall just prior to Christmas. It takes longer to get to the destination. Additionally, one is weakened by the effort and exhausted by the time the purchase of a single item is accomplished.

So, one wants to photograph at the ideal atmospheric pressure to obtain images made by the less exhausted photons. Energized photons produce better photos.
--Bob