The interest saved column is the total amount saved over the lifetime of the loan, not a recurring monthly savings.

Using your example, a 3000 extra principal payment at month 1 saves you a total of 4080.74. However, a 3000 payment at month #243 saves you a total of $98.96.

If those were the only two extra payments made, you would have saved 4179.70 upon completion of repayment.

Does that explanation help? Is there a way to explain or represent it more clearly?