Some graphing calculators have CAS features. Standard graphing calculators, such as the TI-83 and TI-84, are allowed. There are several companies that manufacture models of graphing calculators. There are five calculators in the 49/50 series of HP graphing calculators. Such architectures were used in early microprocessors, pocket calculators and pocket computers. They are used in various electronics like watches, calculators, and notebook computers. Blind people may use talking equipment such as thermometers, watches, clocks, scales, calculators, and compasses. With the ready availability of calculators and computers, rating systems have been introduced. Like some of HP's desktop calculators it used RPN. The 1970s saw the emergence of 4-bit software applications for mass markets like pocket calculators. It was used in early handheld calculators. The evolution culminated in the 1970s with the introduction of inexpensive handheld electronic calculators. The graph above can be compared with those generated by many retirement calculators. Compact solar cells for devices such as calculators and watches are typically measured in microwatts. The following keys are common to most pocket calculators.