I'm for using shared variables, DBlank is for running totals. From watching, the ideas are similar. Since you are calculating for an individual, you would want a reset in there, but it would most likely be at where a 'week' is defined to start. Regardless, the concept is the same, you know the data and the report...
in a group header usually, a reset
shared numbervar OT := 0;
""//hides the zero on the report
in a group footer, a display
shared numbervar OT
usually in the details, the incrementor
shared numbervar OT;
if hoursWorked > 40 then OT := OT + (hoursWorked - 40);
"" //hide the calculation (or remove to display/debug)
the tough part in the line above is how to define hoursWorked.
HTH