Crucible and pre-measuring

I wouldn't normally consider a CoM anyway, but a friend's putting together a psyker-heavy CSM list. I'm normally the most outspoken against pre-measuring, but with CoM it wouldn't be so bad.
Question is, am I allowed?
Just to refresh, codex says:

"Once per game, in the Shooting face, a model with a Crucible of Malediction may choose to open it instead of firing. Every psyker within 3D6" of the bearer must pass a Leadership test or be removed from play"

That to me suggests you can not pre-measure, but then again so do all of the shooting rules except where it says "you can pre-measure" (seethe).

Reckon? Can you pre-measure for distance but then have to roll the dice after declaring you're opening the crucible? Can you measure AND roll before deciding? Pre-measuring is so damn stupid.

You are allowed to premeasure to see how far the enemy is from you, just as you would when rolling for charge range. That information could then factor into your choice of whether to use the Crucible or not, based on whether you think you'll roll high enough.
But once you roll, the Crucible is used.

Ah, makes sense. Good comparison, thanks!

You are allowed to measure any distance On the table at any time. No restrictions.

Yeah, restrictions on pre-measuring are left in 5th.

Just as a smart way of calculating distances, eye-balling etc...