This version of the Linear Regression Channel with Standard Deviation (STD) and Standard Error (STE) bands has dynamic lookback for its calculation.

You can define in the setting a precise date and time to anchor the start of the channel, so its length evolves as time passing by. It can be useful to spot potential breakout of a defined trend or rebound on the top and bottom of the channel.

The original version with fixed bars lookback can be found here: Standard Deviation & Standard Error Linear Regression Channel

//PRC_StdSte LinRegChannAnchored | indicator
//Standard Deviation and Standard Error with date&time anchor
//Linear Regression Channel
//28.06.2019
//Nicolas @ www.prorealcode.com
//Sharing ProRealTime knowledge

defparam drawonlastbaronly=true
defparam calculateonlastbars=1000
// --- settings
AnchorDate = 20190628 //Date anchor YYYYMMDD format
AnchorTime = 050000 //Time anchor HHMMSS format
ChannelType = 1 //1= Standard Deviation ; 2= Standard Erro
NbDeviation = 1 //Deviation multiplier
colorRed = 255
colorGreen = 255
colorBlue = 0
// --- end of settings

if date=anchordate and time=anchortime then
 startbar=barindex
endif

lookback = max(1,barindex-startbar)

if lookback>0 and date>=AnchorDate then
 sumx = 0
 sumy = 0
 sumxy = 0
 sumx2 = 0

 for cmpt = lookback downto 0 do
  tmpx = cmpt
  tmpy = close[cmpt]
  sumy = sumy+tmpy
  sumx = sumx+tmpx
  sumx2 = sumx2 + (tmpx*tmpx)
  sumxy = sumxy + (tmpy*tmpx)
 next

 n = lookback+1

 if (sumx2 = sumx * sumx) then // protection to avoid infinite values
  b = sumxy - sumx * sumy
 else
  b = (n * sumxy - sumx * sumy) / (n * sumx2 - sumx * sumx)
 endif
 a = (sumy - b * sumx) / n

 drawsegment(barindex[lookback],a+b*lookback,barindex,a+b*0) coloured(colorRed,colorGreen,colorBlue)

 //channel
 if ChannelType = 1 then //Standard Deviation
  dat = std[lookback]*NbDeviation
 else
  dat = ste[lookback]*NbDeviation
 endif
 drawsegment(barindex[lookback],(a+b*lookback)+dat,barindex,a+b*0+dat) coloured(colorRed,colorGreen,colorBlue)
 drawsegment(barindex[lookback],(a+b*lookback)-dat,barindex,a+b*0-dat) coloured(colorRed,colorGreen,colorBlue)
endif

return