DBate, it still doesn't work. A jet doing about 145kts on final approach on about a 3 degree slope needs a ROD of about 800 fpm. According to your formula, 3% x 60= 180 feet per mile. At about 150 kts, that's 2.5 x 180=450 fpm which is way too low.
The only formula I ever bothered with on a 3 degree slope is 5 x GS as a rough guide. Being lazy, I didn't do a calculation. Just set a baseline of 800 fpm and adjusted it up or down for slope, unusual GS etc. Why fill your mind with all that jazz when you have other things to concentrate on?