In table views (grids), our CRM web app indicates the column that provides the sorting order by inserting a little A-z or Z-a icon. The app remembers the columns that provide the secondary and tertiary sorting order but does not indicate them in any way on the interface. When designing the interface, we took it as a deliberate decision.
Now we have a few users who want to see which columns provide the secondary and tertiary sorting order. I looked through the pattern libraries but did not find anything. I also searched the web.
I do not particularly like any of these options. Neither is a natural indicator – users need additional information to understand what the images, colors, or numbers mean. I will appreciate suggestions and/or links to information.
Has someone tested how users react to multiple sort-order indicators in a grid?