depending on the detail desing of the form, eg how "column 5" is populated, what you are trying to do with the command button.....
you need to insert the code into selected events
the events to be looked at are:-
the forms "on current", set when the record changes / is re-displayed
the control for "column 5" lost focus event
you mnay also need to insert the same function call in the forms before update.
if "column 5" is a boolean (yes/no) value then you could set the code in the controls on change event,
just as an aside I presume your are NOT using "column 5" as the name of the column in the table. Lots of reasons, first of which is try to give a more descriptive or meaningfull name for the the column which represents the data actaully stored in the table also try to avoid using a space in a column name (it can cause problems with soem SQL implementations).