I am currently playing arithmetic back(PASAT). I think that if it gives you the right answer after you indicate a wrong option it would speed the learning process. For instance if it gives you 7 and then asks you divide 8, then when you select the wrong answer it would put .875 in red. I think this is helpful because the program is constantly reaffirming the correct answer when you make a mistake, especially conducive under time constraints and uncommon equations. I am not sure if this would negatively affect transfer of the program, but in many cases arithmetic is a memory based system. So for many of the common equations memory is used to speed the process and bypass the use of logic to figure out the equation on its own. Certainly over time as well the end result of training would be an almost complete memory bank of possible equations as well. As repeats of equations is unavoidable. With the individual memory bank of equations increasing with time.
Furthermore I also wanted after some research of the PASAT, to state that the arithmetic back is one of the most benefical n-back programs to execute. This is due to its ability to stimulate the anterior cingulate, superior temporal gyri. Areas of the brain located in the left hemisphere, which certain clinical studies show that PASAT strengthens the transmission of knowledge.
I take this to mean that it stimulates areas of the brain that are not stimulated during regular n-back. with the inclusion of triple arithmetic back, though some of the same areas of the brain used dual and even triple in n- back are also used in the arithmetic back program.
Therefore triple arithmetic back has the greatest variety of brain areas affected during training.
I will say though that the flexibility quotient cannot conceivably be at a greater level than quad or pentuple or pentuple +multi stim.and I have no evidence to substantiate its comparison to combination back.