I've mercury folded cards since the 1960's and I'm now using Jon Allen's Perfect Score.
Even if you practice folding 5k decks of cards, when performing, your Mercury fold will be off.
If it has to match a previously folded card, it needs to be perfect. That's were Perfect Score
comes in.
You can do one card to be forced, or do an entire deck so they have a free
choice. The scoring is so precise there will be nothing to see out of the ordinary.