I feel like I understand the red and green parts of the lines for transferring the height of the reference person up and down the steps and further down the steps towards the background, but still don't understand what the blue line in particular shows, especially since the blue line first traces the three lower steps, but then goes straight up into the air for the 4th step. If it's tracing the steps for the first 3, why doesn't it continue for the 4th step like this yellow line? I feel like if I understood why it doesn't turn for the 4th step, I would understand its purpose/meaning!
Also, how are you drawing lines on the drawing? I would like to get that app. The one I have on my phone is not very easy.
And yes, would love to hear the non-basic explanation for predicting the end of the step above the horizon line. I might find it in my old architectural drawing class notes, as well, as I go through the rest of the exercises for the week.