Saddle height? Inseam minus 10cm?

Been feeling like perhaps my saddle is a bit low... so had a quick trawl through past posts and found this.

My slightly dumb question is... is the height calculated on the perpendicular? IE measure from centre of BB straight up at an angle of 0 degrees, to the top of the saddle? Or, should I measure along the tube, which looks like it runs at 5-10 degrees? There's a 4cm difference by my calculation.

Work out your length. Then measure in a striaght line from the BB centre to the 'sit-bones' area of the saddle.

So no, not perpendicular. But not always in line with the seat tube either.

I find being able to extend my heel ~1cm lower than the pedal axis. With the pedal at its lowest point, and with my botty central on the saddle. Is a decent guide for road ridng.