B777 legs page - building a waypoint
 

Wanted to build a point 100 nm before 69N060W. That waypoint was L line selected into the scratchpad.

The following were rejected :
69N060W-100
69N060W/-100

I believe - but cannot be 100% sure - that we were more than 100 nm away from 69N060W.

What is the correct format ?

In which manual can I find the correct format ? FCTM ?

If it's like any other Boeing, put the original waypoint in the LEGS page, press the LSK next to the waypoint (so it comes up in the scratchpad) and add "/-10" to the scratchpad and add the waypoint before the original one.

Your waypoint format is not correct. I should be 6960N then add /-100 to give you 6960N/-100. As you noted, you must be beyond 100 nm from 6960N.

It's page 11.31.12 in my 777 FCOM

You can also put that wpt into the fix page then put a /100 ring around it. Line select /100 and the scratch pad will give you a new designator for the point where your ring intersects your track. Then put in in the legs page.