Pohlmann-Mass method
Step A: If the integer is 1,000 or less, subtract twice the last digit from the number formed by the remaining digits. If the result is a multiple of seven, then so is the original number.
Isn't this step enough to check divisibility by 7 for all numbers. But then why wikipedia mentions step B for numbers greater than 1001 as following.
Step B: If the integer is between 1,001 and one million, find a repeating pattern of 1, 2, or 3 digits that forms a 6-digit number that is close to the integer (leading zeros are allowed and can help you visualize the pattern). If the positive difference is less than 1,000, apply Step A. This can be done by subtracting the first three digits from the last three digits.
Where step A fails?
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