The DRAW_NONE style is designed for use in cases where it is necessary to calculate the values of a buffer and show them in the Data Window, but plotting on the chart is not required. To set up the accuracy use the expression IndicatorSetInteger(INDICATOR_DIGITS,num_chars) in the OnInit() function:
The number of buffers required for plotting DRAW_NONE is 1.
An example of the indicator that shows the number of the bar on which the mouse currently hovers, in the Data Window. The numbering corresponds to the timeseries, meaning the current unfinished bar has the zero index, and the oldest bar has the largest index.
Note that despite the fact that, for red color is set plotting #1, the indicator does not draw anything on the chart.