If I recall correctly, the N1 information is sent to the DEEC (digital electronic engine control) that in turn controls the fuel control solenoids. Hence the term "N1 DEECS".....the DEEC can be downloaded by a PC
by an engine trend monitoring program called ECTM that Honeywell distributes. It is an excellent program that allows you to track every engine parameter, see exceedances, and also troubleshoot. I used it recently to track down a bad engine wiring harness....it had an intermittent short at the "A" solenoid.
Not to correct Dougloid, but I think the N1 monopole is mounted on the accessory gearbox. I changed one once or twice on a Hawker 800XP that had the -5BR engine. You had to verify the proper distance between the face of the monopole and the gear in the AGB
it was looking at with a depth micrometer and shim it accordingly....