not routinely used -- batts out till needed. Went to add a list of items purchased, and then add sales tax. Had the total, then hit PLUS, then 7, then %. It gives the wrong answer. EXAMPLE; If 1000, 7% is 70, so total = 1070. If you take 1000 x 1.07, it IS 1070. If you take 1000 PLUS 7% it claims 1075.28817. Tried 4 other small calculators -- all give 1000 PLUS 7% as 1070. Whatsamatta??!!