down to a gnat's eyebrow
In consideration of the most minute detail. I have planned this itinerary down to a gnat's eyebrow, so we are not deviating from it, even for a minute!
down to a gnat 's eyebrow
Fig. down to the smallest detail. He described what the thief was wearing down to a gnat's eyebrow. No use trying to sneak anything out of the refrigerator. Mom knows what's in there, down to a gnat's eyebrow.