Nice refresher
Thanks from me, too. I couldn't remember, either.
It's just a proportion, as you learned in high school.
Here's a cool one you can use to calculate rate of descent on a standard three-degree glideslope.
First, you have to know your groundspeed. Let's say you use a 90-knot IAS as your standard approach speed. Then, you have a 10-knot headwind component. So what rate of descent do you set up to hold the glideslope?
Place 3 over the 60 pointer on your whizwheel. Your groundspeed will be 80 knots (90 kts IAS - 10 kts headwind). Look for 80 on the bottom scale and look up. You'll see 40, which represents the 400 fpm descent you need to commence when the glideslope needle centers.
That one courtesy of my Alitalia students and their training captain at FSI.