Finding items on the desert map, 4-3

[caleb723]

Is there a certain formula or something that's used to give you the chance at finding the items?  My Sanaki spent ~10 turns with her 39 Luck (Paragon + BEXP abused her to 20 >_>) trying to find the White Gem, but Naesala with his 22 Luck (or so, I can't remember for sure) found both the Baselard and the Laguz Gem in only one turn.  Even Micaiah with 40 Luck had a little trouble finding the Daemon Card.  I know Luck gives a chance, but all I wanted to know was if we could actually find that chance ourselves, so it'd be easier to plan my moves on that level.  (Sanaki kept getting surrounded, because I was positive that next turn she would find it and I could get her outta there with Sigrun or something.)

Actually, on that note, is that same formula used to get the other items, like the Arms Scroll in 2-3 or the Ettard in 3-4?

Thanks for any answers in advance.  If I need spoilers tags or anything, (which I figured I didn't but you never know...) Let me know and I can do that.

[Shirona]

Surprisingly, it's actually Skill, not Luck...

According to SF: Skill + Thief Bonus + Biorhythm bonus [%]
Thief Bonus: 60 if user is a Thief, Rogue or Whisper
Biorhythm bonus: +20 if arrow is pointing at highest, +10 if pointing at high, -10 if pointing at low and -20 if pointing at lowest

And yes, it's the smae rate for all chapters.

[caleb723]

I was told by multiple people it was Luck and not Skill...

That clears up a LOT.  Thank you very much Shirona.