. . . mid 90 as suggested in an earlier post . . .
Well according to the checklist the horn is supposed to come on below 97%. So by setting the rpm to mid-90's and raising the lever a little bit the horn should come on. I then engage the governor and check that the horn goes off at 97%, and then check that the governor stabilises the rpm at 104%. This is an efficient way of doing the checks, minimises time at full revs before lifting and saves fighting the governor to lower the rpm.