Nope, he still cannot grasp the concept. Rayzor I think you are wasting your time, basically trying to have a discussion about precision equipment to someone who has the mentality of a 8 year old.
I suspect you are correct, but I know lots of 8 year olds who can grasp the concept of level and straight.
Now I will ask you again, how are you determining your right angles. Could you demonstrate how you are achieving that on your spherical model.? Lets dumb it down for the punters & use a spoked wheel for a basic exsample. Now lets apply one side of a engineers square to the edge of the spoke . The other edge giving us the right angle , to shoot our straight line from . Are you phucken crazzy or just plain retarded. ?
Ok let's try again, you know that the spokes of a wheel are not parallel, let's go with that, the precision levels work using pendulum's with sensitive electronics to detect microscopic movement, the measurement is in terms of the angle of the instrument to vertical ( one spoke of the wheel ) now we find that with two levels ( a differential pair) moved apart by 50 meters, so each one measuring a spoke on the wheel. If the earth was flat the angles would be the same. That's not we find at all, we find there is a difference in the angles which reflects the earth's curvature. Since the curvature we measure is convex, that measurement rules out concave earth theories also..
Over the distance of 50 meters we should see about 1.62 arc-seconds which works out to a wheel radius of 6300 km give or take. Funny, that's the radius of the earth isn't it.

Direct optical earth curvature measurements are disputed by the concave theorists, who insist light travels in curved lines which creates the illusion of convex earth. This method doesn't use optical instruments and therefore eliminates the concave earth theory once and for all.
That's it, happy to answer any further questions, just leave the insults and ranting in the playground.