At the moment the CoC sheet offers a separate roll for bonus/penalty dice after a skill check. The output of that roll is... improvable. Currently it just shows the outcome of one 1d10 roll, nothing else. There is no real distinction between bonus and penalty although the code asks. Much better solution would be to show something like "original roll (percentage), bonus/penalty roll (percentage - the lower d10 is the same as original), result (pass/fail)". The data are all present, so this shouldn't be much effort.