Agreed, to me, it looks like its at 80, right at the very top of the green stripe.
May be worth investing in digital thermometer?
I use cheap digital ones that is wired to a probe that goes into the tank and the display part can be anywhere on the external side of tank glass you want. Appears to be pretty reliable so far, I have one of these on all 3 of my tanks.
Idk about digital, I'm pretty low on funds, I can read it just fine, I even did the "thermometer test" if you've have heard of It, and it turns out it's a good thermometer, perhaps nextime I'll purchase it