Column to show number of men required?

As you have discovered only fields from the activity table can be displayed in an Activity layout, and what p6 calls "units/time period" is in the Resource Assignments table.  Of course that means you CAN display that value in a Resource Assigmment layout, but you cannot display a barchart.

You can use Global Change to divide "Budgeted Labour Units" by a value - but what to divide it by?

If you divide by duration, the number it uses is the hours stored.  It does not read the activity calendar, indeed there is no way to do that. Once you have the BLU/OD sum stored in a user defined field , you will then have to consider is there are multiple shifts involved.  A duration of 24 hours with 24 hours of labour would give an answer of 1 when you do the first global change, but it might require three people to do 24 hours work in a day. 

number of men based on what ?

do you have resources and budgted labor units assigned for each activity ? if you do then you can create a user defined field.

then export the remaining units/time and the newly created udf to excel

then in excel create a formula that divides the remaining units/time by 8 to give your your # of men for your udf filed then import back into p6. In the formual for the udf value remember to copy past value special for the udf column before you save it 

Zoltan,

what about part time assignments when resource spends certain percent of work time on one activity and the rest on another?

What if the crews are different at different shifts?

What shall be done to find resource requirements on summary activities different at different moments?

Dividing by 8 does not show true quantities.

Vlad 

then the best way to do this is to use either the resource usage profile or the resource usage spreadsheet in p6 

Vlad 

then the best way to do this is to use either the resource usage profile or the resource usage spreadsheet in p6