How to stretch a rotated object in Layout

I’m trying to draw portion of a section reference line, and afterwards stretching it the right length.

While drawing I get perpendicular (pink, magenta…) references. Afterwards, clicking into the object, when trying to move one line segment along another, so to stretch it smaller, I get no such reference, only the red-green can be referenced ? What am I missing?

Not perfect maybe…

inference

I understand. You collect, in a way, the perpendicularity, from that other line. Thanks.

Some more fiddling with geometry. When moving an object I get presented with several suggestions of perpendicularity and other suggestions of red/green direction movement that dont mean much to me…

May I suggest that @TheOnlyAaron explains these mystical phenomena in a YouTube “Square One” video?