Originally Posted by edc1
i wasnt aware it was flawed i use the 42 rule its fast and easy it doesnt have to be perfect to be effectivei do like four dogs expelenation of it seems like its spot on


its only slightly flawed, unlike OP who said seriously flawed.
When you have more than 8 outs it isn't as accurate, i.e. if you have 15 outs on the flop with an OESD and Flush Draw you have 15 outs but that isn't 60% (15 * 4)
There is a modified version whereby every number over 8 you subtract that from the final total, so in example above
15 outs x 4 = 60  15 is 7 above 8 so take off 7 and the answer is 53%
See pic below and compare the actual odds (Turn or River) to the 4 2 Rule column and Modified column. As you can see the difference gets bigger in the normal 4 2 Rule, whereas in the modified it stays pretty close.
At 20 Outs Actual is 67.53, 4 2 Rule is 80 and Modified 4 2 is 68