Hi "A Mile Of Sky",
thank you for your message!
If you see a place for the first time, it's actually difficult to choose the staff gauge that's fitting best. Sometimes you can see from the surroundings if the waterlevel is very low or very high (and then you can choose the green or red gauge). But usually if it's a place that you don't know so well, it's a good idea to just choose the yellow gauge. This way, you will have room upwards and downwards for water level changes.
If you can choose, it's usually best to initialize a spot while there is low flow. It's easier to determine the water level class while updating when the reference in the background is visible and not hidden by water in the root spot picture.
I hope I helped you with this reply
Have fun spotting! Best,