Jeff and Craig, thank you for answering my question.

@Craig: The suggestion of using a report is not possible, I am sorry.

I made a report function in my Delphi program, in which I can place a Sql-instruction.

When they push a button it produces an Excel result.

@jeff: The quirky update solution is to difficult for this use, I am sorry again.

The user wants a list of the amount of bookings per week.

I use the excellent isoweek solution of Jeff (I am so happy with this publication).

There are not so much bookings in a year (a max of 5000), and after a year al bookings are written to a history file and it starts again from zero.

A simple COUNT(*) and a GROUP BY IsoWeek, gives the user the most recent bookings per week.

Knowing that adding a running total is difficult, I'll only add a grand total, that's what the user gets.

Thank you for your effort