Note that it is rare that someone would need to change their X or Y steps.

That said, this is a simple one-nozzle-width, one-layer-high square test model to check their accuracy. Measure the distance between the line centers, keeping as perpendicular as you can (measuring near an edge makes this easier). The rationale is that even with Z height differences and flow variations a single line is going to be pretty symmetrical and that the large distances this approach offers will help compensate for any asymmetry and the inevitable measuring errors. If it's really close, your printer is probably fine as is. Your call as to what matters, but I personally wouldn't worry about an error less than 0.5%, especially given the limitations of this method (mine measured at around -0.2%).

200 mm and 150 mm models are included in both 0.4 and 0.6 mm line widths. The Fusion 360 file is also available so you can make your own sizes by changing the parameters. If you aren't familiar with Fusion 360 and want another square size or line width, ask in the comments and I'll add it the next time I get a spare moment.