for high-contrast is available as well (NW240AA). The form and size of the calculator shell is identical to the 49g+ series, but four AAA batteries are used as opposed to three in previous models. In addition to all the features of the 49g+, the 50g also includes the full equation library found in the HP 48G series (also available for the 49g+ with firmware 2.06 and above), as well as the periodic table library originally available as a plug-in card for the 48S series, as of firmware 2.15/ 2.16 (the latest, as of 2015), and has a 3.3V TTL-level asynchronous serial port in addition to IrDA and USB Mini-B ports of the 49g+. Like the 49g+, the range of the infrared port has been limited to about 10 cm (4 inches). The asynchronous serial port is not a true RS-232 port as it uses different voltage levels and a non-standard connector. An external converter/adapter is required to interface with RS-232 equipment. The keyboard, the most often criticized feature of the 49g+ calculators, uses the new design introduced on the very last 49g+ calculators (hinged keys) to eliminate previous problems. A worldwide announcement regarding the availability of this calculator was made by HP in September 2006, and official details were available on the HP calculators webpage. The calculator was officially discontinued in 2015. Programming The HP 49/50 series of calculators support both algebraic and a stack-based programming language named RPL, a combination of Reverse Polish Notation (RPN) and Lisp. RPL adds the concepts of lists and functions to stack-based programming, allowing the programmer to pass unevaluated code as arguments to functions, or return unevaluated code from a function by leaving it on the stack. The highest level language is User RPL, consisting of sequences of built-in postfix operations, optionally including loops and conditionals. Every User RPL command checks the stack for its particular arguments and returns an error if they are incorrect or not present. Below User RPL is System RPL (SysRPL). Most System RPL commands lack argument checking and are defined only for specific argument types (e.g. short integer vs. long integer), making System RPL programs run dramatically faster than equivalent User RPL ones. In addition, System RPL includes many advanced functions that are not available in User RPL. System RPL programs can be created without the use of PC software (although it is available), thanks to the calculator's built-in