This idea first formed when I wanted to write an SCP that looks like one shape but is actually another. Over time, this idea took shape (ha) as an equilateral triangle that looks completely normal until you measure its angles with a protractor, at which point you would find that it's composed of three right angles.

At first, I thought I could use the fact that a shape drawn on a curved surface has different angles than it does on a flat surface, and mention something about how the blank side of the paper doesn't actually exist. But I feel like dimension-bender SCPs have been done to death by now, so I'm thinking that a perception-bender might be more interesting.

Right now I'm thinking that this triangle appears to have three right angles only when measured with a protractor, and only when the person doing the measuring is personally invested in getting a correct answer. This would put some interesting limits on what the Foundation could discover at first; since they're scientists, most of them would probably genuinely care about what the angle is, and therefore, they'd all end up measuring it as 90 degrees. Initially, they'd probably hypothesise that it has dimension-bending properties, because the results would be consistent among researchers, thus suggesting something that messed with reality instead of perception. Then, upon doing some experiments*, they'd discover that it wasn't bending dimensions at all, and start expanding their tests, eventually having people with no mathematical interest measure it. When they find that some people can measure a sixty degree angle just fine, they'd start looking further into it. I'm thinking maybe one of the subjects could flippantly remark, "I don't honestly give a damn what the angle of that triangle is," and cause a researcher to have an epiphany, I don't know.

*These tests would consist of putting protractors on two angles at once and using another protractor to measure the angle between those two protractors. This test would give them a measurement of 90 degrees for the two protractors on the triangle, and 60 degrees for the third, since it's not directly measuring the triangle. Another test that would give them a mathematically possible result would be if they traced over the triangle on another piece of paper, cut that triangle out, and put it back on top of the anomalous triangle; the angles would match up just fine, since the SCP only messes with measurements made by protractors.

This SCP could also be written as a joke SCP if, instead of 90, the angle measured was 69.

Is this idea original enough to be an SCP? Are there any cliches or logical failures that I'd need to fix? And how can I structure the article as far as experiment logs/addenda go?

(edited to collapse it)