Pythagoras and Aristotle argued that the Earth was round based on observations such as curved shadows on the moon during eclipses and ships disappearing over the horizon. These are qualitative arguments much as your “I can’t see any curvature” is. Eratosthenes, in the third century BC, used the neat little trick that you could do yourself today. He measured the shadow cast by a vertical object at two different locations (Syrene and Alexandria) and then used his observations and maths to calculate the circumference of the Earth. If you care you can look up the details. P and S waves, the waves created during an earthquake, can be used not only to show the Earth is round but they also help us to understand what the earth is made of. Again easy to look up and find explanations for if you care to. Your comment about using a spirit level to show that the Earth is flat is fundamentally and technically flawed. If you wanted to use a spirit level to show that the Earth was flat the level wouldn’t need to be over 200m long. Look up the Sagitta formula if you care to know why. The mistake you have made here is not taking into account the relative scales of the thing that you are trying to measure and the thing that you’re measuring with. You can use a similar method such as shining a laser beam over 500m or so to demonstrate the Earth either being flat or curved and the results are consistent with a global not a flat earth. Again using these observations and a little maths, you can calculate the curvature of the earth. You can use a sextant to measure the angle above the horizon of Polaris. In the northern hemisphere as you travelled further south Polaris gets lower in the sky. This observation is consistent with a globe Earth and, again, with some measurements and the little maths you can calculate the curvature of the Earth. I’ve giving you 4 examples of Observation + measurement + maths = proof in support of a globe earth and explained why using a 30 cm spirit level does not work to show that the Earth is flat. Please help this max retard understand the error of his ways by giving me comparable proofs that the Earth is flat.

you have given just linguistics, in science we are talking about practical/physical experiments - its ridiculous i have to spell this out to you - you cant touch or adjust any parameters of a horizon (its just the vanishing point of your vision), a shadow or an earthquake sine wave are just obaervstions you add some maths too which is just a language as i already told you.. 😅