Data loggers and data recorders acquire digital data from sensors and other signals. They are primarily used to store data for subsequent downloads to a host PC, but may also include real-time features such as monitors and alarms. Important specifications to consider when searching for data loggers and data recorders include differential analog input channels, digital I/O channels, sampling frequency, resolution, and accuracy.  Differential channels use the difference between two signals as an input; common mode is filtered out. In some systems, differential inputs are combinations of two single-ended inputs; in this case, twice the number of differential channels would be available as single-ended inputs.  Digital or discrete channels are used for low-level on-off signals used in applications such as communication, user interface, or control.  Sampling frequency is the frequency of the analog signal sampling and conversion to a digital value.  Resolution refers to the degree of fineness of the digital word representing the analog value. A ten-bit number contains 2¹⁰, or 1024, increments. A 0-10V signal could therefore be resolved into approximately 0.01V increments. A 12-bit representation would be in 2¹² (4096) increments, or divisions of 0.0024V for the same signal. Each additional bit doubles the resolution, and one bit is required for the polarity (sign) of a number.  Data loggers and data recorders accuracy depends on the signal conditioning linearity, hysteresis, temperature considerations, etc. It is represented here as percent full scale of measurement range.