characters on most of the rest. The displays also included some way of indicating operational mode, scientific mode, and other states and conditions. The Casio models included lower-case characters. These were only for use in PRINT statements, as lower-case commands and variables were not accepted as with almost all BASIC programming machines. In general, the two specific lines were not cross-compatible, but there were compatibilities within lines. PC-1 programs would work unmodified on the PC-3 and on the PC-8 with changes for screen size, and PC-4 (26-3650B) programs would run unmodified on the PC-5, PC-6 and PC-7. The PC-2 was a unique architecture and was the only unit in the line allowing direct memory access with POKE, PEEK and CALL. Operating modes Each model had two operating modes: Run and Prog. Run In Run mode, the command line could be openly used to execute one-line, non-BASIC operations. This is the normal mode used, from where arbitrary calculations could be entered to receive results. The Run mode also allowed the execution of the BASIC programs stored in the device. Instead of an "equals" key to initiate calculation evaluation, an "EXE" (execute) key was provided. This caused confusion with those who were used to traditional calculators. The = character was used only for variable assignment, and evaluation tests in programs. The input of simple calculations would be aggregated on the command line, and no results would be displayed until the EXE key was pressed. In some models, a special ANS variable was provided to reuse the results of the previous calculation; in others, the previous calculation was automatically included if the next calculation began with an operator. Some valid calculation input examples (PC-8): SIN40 10+2+(8*1)/7 TAN (LOG (√(4/3))) Prog The Prog mode changed the input from a command line to a program editor. In this mode, BASIC programs could be entered one line at a time. Up and down arrow buttons were provided to scroll up and down through the program space. On most models, free calculations could not be entered in the Prog mode. Certain models, especially the Casio-derived ones, called this mode WRiTe mode. On the Sharp models, there was only one line numbering space. In order for multiple programs to exist on the device, they had to be written in different ranges of line numbers. For example, it was common to insert one program starting with line 100, and