Trust your eyes when it comes to the plumb-bob technique. To the naked eye, you may have a hard time seeing the break, but if you see it when you plumb bob, you know it's there.
Take 15 minutes before your match to work your way around the practice green while using the plumb-bob technique.
Walk up to your ball after you plumb bob, take one practice swing and putt it. Golfers who take multiple practice swings and take 20 seconds or more to stand over their ball and contemplate the putt usually end up missing.