You can add a formula field calculating the percentage of each record to the total using the SUBSET_SUM function, then set the bar view to show this field as its value. Please see attached for an example.

For simple percentage representations, better to use the Pie view, where % is calculated/displayed automatically.

Hi Edward,
Thanks for the solution.
My problem is that the sales of each individual brand are on the monthly basis,I want to get the % of contribution over the selected month. I guess in order to do this , i have to calculate cumulative sales of each brand over the month, then divide by the cumulative total sales. is it possible to do this on omniscope
Thanks,
Xuan

This can be done with the SUBSET function by defining a subset called Month. Please see the attached.