Had another look at the MS code for the trailing stop and put together some AFL that looks like it will do the same job. Copy and paste into Formula Editor then click on "Apply Indicator". Will plot the trailing stop as a red line. Drag and drop a price chart on top. Can adjust lookback period and percentage stop by right clicking chart and selecting "parameters".
Code
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lookback=param("lookback",20,1,20,1);
percent=param("percent",7,1,10,1);
stop=hhv(close,lookback);
sellstop=stop-(stop*(stop/100));
Plot(sellstop,"sellstop display",colorred,styleline);
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Cheers,
The Captain