Eli5: Saline drip volume markings


Why are the volume markings on [this drip](https://en.m.wikipedia.org/wiki/Saline_(medicine)#/media/File%3ANaCl_0%2C9%25_500ml_white_background.jpg)not uniform, eg the distances between 0-100, 100-200, 200-300 are so different?

In: 0

If I am not mistaken it is because the liquid will be let out but air will not be let in. So the bottle can bend and will change shape. The change in shape results in an uneven distance. You do not let air in to reduce the risk of any contamination.

Because the bag isn’t a uniform size up and down the length of it. The saline solution deforms the shape