Every decoder works fine when errors are rare. Crank the physical error rate up and eventually even a perfect code drowns. This module runs a real Monte Carlo experiment, sample thousands of random errors, decode each one with a real decoder, and measure how often a logical error slips through. Then sweep the error rate across code distances to look for the threshold: the crossover where making the code bigger finally starts helping.
The ideal: below a critical error rate, the curves should fan out so that bigger distance = lower logical error rate (d=7 under d=5 under d=3), and above it the order flips. That crossover is the threshold. The reality at this scale: distances 3 to 7 with a few hundred trials are small and noisy. Real threshold plots use distances up to about 25 and millions of shots. So you'll often see the curves cross in a band rather than fan out cleanly, and at very low p the estimates are mostly Monte Carlo noise. The high-p order-flip is the most reliable signal here. This module shows you the actual numbers, muddiness and all, rather than a cleaned-up cartoon.