Plot standard deviation lines in Pine Script - charts

Question

I have this pine script I'm using on tradingview to plot a line that is the average of the highs and lows of a given time period.
I'd like to plot the standard deviation on the chart of this value:
highLowAvg =(sum(maxValue,length_avg) + sum(minValue,length_avg)) / (length_avg*2)
Is there an easy way to do this? Below is the whole script.
//Fill Arrays with latest LOWS/HIGHS
//Get highest HIGH and lowest LOW values from the arrays.
//Do Average between X highest highs and X lowest lows and plot line (Length can be modified)
//If price LOW is above line, Up Trending (Green) (Source can be modified)
//If price HIGH is below line, Down Trending (Red) (Source can be modified)
//If neither above, slow down in trend / reversal might occur (White)
study("Low - High Simple Tracker",overlay=true)
////==================Inputs
length = input(8)
length_avg = input(8)
up_Trend_Condition = input(high)
down_Trend_Condition = input(low)
stdev = stdev(highLowAvg, length)
////==================Array setup and calculations
lowArray = array.new_float(0)
highArray = array.new_float(0)
//Fill Lows to an array
for i = 0 to length-1
array.push(highArray,high[i])
//Fill Highs to an array
for i = 0 to length-1
array.push(lowArray,low[i])
//Get the highest value from the high array
maxValue= array.max(highArray)
//Get the lowest value from the low array
minValue= array.min(lowArray)
//Average between highest and lowest (length can be modifed)
highLowAvg =(sum(maxValue,length_avg) + sum(minValue,length_avg)) / (length_avg*2)
////////==================Plotting
colorHL = down_Trend_Condition > highLowAvg ? color.green : up_Trend_Condition < highLowAvg ?
color.red : color.white
plot(highLowAvg, color =colorHL, style = plot.style_line, linewidth = 2)