instant center

On a macpherson strut suspension, the line from the top of the strut mount to the instant center, is it perpendicular to the line from the ball joint to the center of the top mount? Or as stated in the tutorial, is it perpendicular (the actual line you draw is parallel) to the top of the strut mount? I'm confused.

It's perpendicular to a line from drawn through the lower balljoint and the centre of the strut top which is usually going to be close to (but not quite the same) as the angle of the mcpherson strut. I'll check back through the module as I'm pretty sure that was how we explained it and drew it.

The reference line for instant center location on a strut car is drawn perpendicular to the strut, not the line from the lower ball joint to the strut mount.

Here is a reasonable description. https://suspensionsecrets.co.uk/roll-centre-and-roll-moment/