Constructing Error of Pressure Machine

Dear MLC,

I read pressures from a gauge:

p = [789 654 87.5 65.9 12.9 3.24 1.02]; % torr

and I'd really like to be able to reliably get the errors--half of the next digit of significance that is not shown.

I feel like i should use mod somehow but I'm not sure I know what to do except divide by ten.. I'm at a loss. Any help is much appreciated.

truly, Michael