Thanks all for confirming what I was thinking. I've also noticed the clarity of the mash near the end, but I was never confident I was converting all of the starches. I've been trying Kai's efficiency analysis spreadsheet, and on this particular brew it said I achieved 90% conversion efficiency, not bad I guess. I think that even though the liquid is clear, it doesn't mean there aren't starches going into solution and then being converted. I just want a way of knowing when the mash really was done.