Quantity is defined as the step size of the quantization applied to the corresponding signal. It affects the amount of data in the report. Considering performance and report size, you should always use the highest possible value for the quantization step size. The smallest value that the quantity can take on is always the sample rate. This means that the quantity can be only a value > 0. A quantity of 0 or negative values are not allowed and lead to an error.

Note that grid and quantity are different: Grid affects the interpolation of each signal in all measurements. Quantity is the step size of the quantizer applied to the signals in a chart.