/sci/ - Science & Math

So today I got bored and decided to perform an experiment. If the earth is a sphere (as Big Globe wants us to believe) then an observer looking straight ahead at 90 degrees to the pull of gravity should be looking above the horizon, with their view heading off tangentially with the surface of the earth, like in pic related.
In order to test this, I took my telescope outside and stuck a magnetic level rider on it.
I then looked through the telescope and centered it on the horizon, before locking it in place and checking the reading on the level rider (I'm willing to go back out and take some pics if you don't believe me).
No matter how many times I did this, or which of the visible horizons I looked at, the reading on the level rider was always within 1 degree of 0.

So my question is basically, why is this the case. Did I get something wrong, or is the earth really flat after all?