HP 15C
The HP15C is a high-end scientific programmable calculator of the Voyager lineup.
Introduction
Introduced in 1982 and discontinued in 1989 in favor of the Pioneers, it shares the shirt-pocket sized portrait housing with its Voyager siblings. Due to the limited keys available, this model utilized double shifts, marked as f and g and indicating functions printed in yellow and blue respectively, making most functions two-key combinations, with three-key combinations for less used functions like matrix operations and conditional tests.
The backplate details the battery configuration, loop behavior of ISG and DSE, and the common metric to imperial conversions on the first row. On the second row, register usage breakdown for statistical functions, two-argument functions behaviors, error codes, program conditionals and matrix operations are provided. In the bottom right corner is an FCC legal disclaimer.
Features
Functionality wise, it is unique in all HP calculators in having a "complex stack", consuming four register spaces automatically when flag 8 is set.
As with period HP calculators, numbers are stored as 7 bytes (56 bits), 10 digits decimal mantissa plus two digits exponent Binary Coded Decimal (BCD). Internally 13 digits are used for higher accuracy, but the result is always rounded to 10 digits when delivered to the X register.[1] In practice this results in a at worst 9th digit correct result for built-in functions, and at worst 5th digit correct result for individual components of complex result.[2]