Moving Trend Band for Amibroker (AFL)

/*
   Moving Trend Bands (MTB)  [experimental]
   Written 030408We by uenal.mutlu@t-online.de 
   Similar to Bollinger Bands, maybe better?
*/
// mid = LinearReg(C, Prefs(4));
   mid = TSF(C, Prefs(4));

   sd  = StDev(mid, Prefs(4));
   top = mid + 1 * sd;  // check 1
   bot = mid - 1 * sd;

   Plot(C, "Moving Trend Bands (MTB)   C",
     colorBlack, 1 + 8);
   Plot(mid,  "mid", colorRed, 1);
   Plot(top,  "top", colorBlue, 1);
   Plot(bot,  "bot", colorBlue, 1);