"Back in the day" I used a homemade cardboard circular-slide-rule-type final glide calculator. It had distance and altitude scales, an airspeed scale, and curves for different winds. You set the distance and altitude and flew the speed according to the estimated wind. As the checkpoints went by, you adjusted the alt/dist to actuals and rapidly homed in on the approximate actual wind (conceptually similar to a pre-GPS LNAV, I believe). The finish margin was whatever you wanted it to be mentally. This was how REAL pilots flew: i.e., using a Sectional chart and compass.

I still keep it tucked away in my cockpit for sanity checks when my moving map shows me multiple altitude margins, including margin to gliding to the home airport, margin over the edge of the finish cylinder at finish height, margin to the center of the finish cylinder at ground level, etc. And then my CN vario shows its own altitude, which, as T8 helpfully explained, is always different, apparently based on total energy conserved in a pull up.

I can trust cardboard. It only offers one version of the truth, although it, too, can be fooled by sink, as happened twice this year on final glides at the CCSC Std. Nats that should have been straightforward but were anything but.

Chip Bearden
JB