The ‘Drift’ style applies only to the Min-Max chart and restricts any line terminators to the 2nd set of values. This is not necessarily the ‘high’ end of the line, so you can use this option to show movement either upwards or downwards.

ch.Set 'style' 'drift'

This style applies when the chart has either ‘terminators’, ‘arrowheads’ or ‘errorbars’ at the line ends.