HP-12C programmable financial calculator, 1981
A financial model, the HP-12C provides basic business functions including depreciation and date arithmetic. It has become the standard business calculator and is HP's longest-selling calculator. Research indicated that one of the reasons for the HP-12C's remarkable success was that, to many users, a vertical shape meant "calculator," while a horizontal shape meant "computer." Thus, the horizontal HP-12C felt like a computer to users and to their customers who saw them using it. In addition, the gold tone seemed to add a level of prestige to the product.
The HP-12C has become the standard business calculator. It is still sold today.