Under the hood geometry calculations

I create lines perpendicular to a points along a line by calculating the X and Y coordinates of the beginning and ending points.
The lengths of these perpendicular lines differ depending on the slope of the original line at the point of intersection.
Checking for consistency, I clip the perpendicular line by a buffer the of same length as my perpendicular lines should be.
Each buffer is exactly the same area, but my perpendicular lines still differ depending on the slope of the original line at the point of intersection.
Whether drawing or calculating, I cannot get a consistent length for perpendicular lines, they differ by as much as 20% in length.
What is going on?

Spatial reference: 2779
Workspace: dataset