Tek scopes show the following markers:

The small grid is to absolutely pin point the Blue bar in 75% colour bars, the bigger box is to show you roughly where saturated blue content should be - The outermost edge is where 100% lands

The inner and outer circumferential edges are at equal vector magnitude (so same saturation) so curved. The top and bottom edges are flat so are fixed hue (i.e. angle)

The following PDF has good diagrams showing what the 'perfect' scope looks like:

https://download.tek.com/document/25W_7247_1_rfs.pdf