Hi Juan Mena,
You could use a free cell with the last run formula on your report. This would work on Tablet devices as per layout design. This would work for Webi reports.
Note:- If you are using it on a iPhone you will need to attach a free cell to a report part. Please Refer to Report Designer Guide of how to attach a free cell to Report Part. http://help.sap.com/businessobject/product_guides/boexir4/en/631_mobiOS_Repdesigner_en.pdf
Regards
Vikas