Semi-Log charts more or less display price changes in percentages and linear charts work just by the numbers.
There are very strong opinions on which one should be used. Tea prefers linear, and LG and I prefer semi-log.
From what I've seen the vast majority appear to use semi-log charts. If you look at something like CETV on a monthly chart you'll see why semi-log often times makes more sense.
You can choose linear or semi-log by clicking in a box under your chart on stockcharts.
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