An argument is a specific input value passed to a command, function, or subroutine when it is executed. It provides the actual data required for the operation to take place. While the term "parameter" refers to the variable definition within a function declaration, an "argument" is the concrete value assigned to that parameter during a specific call.
For example, in programmable power supply control, arguments specify settings such as voltage or current levels. In the SCPI command SOUR:VOLT 12.5, SOUR:VOLT is the command header, and 12.5 is the argument. This argument instructs the power supply to set the output to 12.5 V. Without this value, the command is incomplete. Similarly, when using a device driver API, a function such as SetOutput(1, 12.5, 2.0) passes three arguments to the instrument: the channel number, the target voltage, and the current limit.
Arguments define the precise behavior of the connected equipment. The data type and valid range for an argument are determined by the device specifications and command syntax (e.g., SCPI or API reference). Sending an argument outside the allowable range--such as a voltage value exceeding the rated maximum--will typically result in a command error, which the control system must detect and handle.