(X*4*Y)/1200

X= BPW and Y=Engine RPM.

TBI IDC (%) = [4 * IPW (ms) * RPM]/1200

Wrong calculation was started here in 2007:
http://www.fullsizechevy.com/forum/g...lse-width.html

Comes out correct to 1project2many TBI helper and all other math...