Getting Bar number of yesterdays low

I very rarely use the bar number for any of my custom projects on Thinkorswim. I really don't have a use for it. I track conditions and values directly. And if I want to keep track of how many bars between conditions I create variables which count those bars.

However one of the things I use very frequently is tracking the lowest low and highest high and carrying those values over into the next trading session. So I can very quickly adapt those techniques to also capture and display the bar number.

For those looking for a detailed explanation on the BarNumber() function you can view the following resource from Thinkorswim:

https://toslc.thinkorswim.com/center/reference/thinkScript/Functions/Others/BarNumber

The following code displays the lowest low as it forms across the trading session. And you did not mention you intended to use this on an intraday time frame but based on the rest of your details I believe that is what you intended. The following code also displays the bar number at each candle which forms a new session low. The label in the upper left corner displays the bar number for the last lowest low of the previous session.

def newDay = GetDay() <> GetDay()[1];
rec trackLowestLow = if newDay then low else if low > 0 and low < trackLowestLow[1] then low else trackLowestLow[1];
rec trackLowBarNumber = if newDay then BarNumber() else if low == trackLowestLow then BarNumber() else trackLowBarNumber[1];
rec previousSessionBarNumber = if newDay then trackLowBarNumber[1] else previousSessionBarNumber[1];
plot lowestLow = trackLowestLow;
AddLabel(yes, Concat("Prior Low Bar # ", previousSessionBarNumber), Color.WHITE);
AddChartBubble(low == lowestLow, low, BarNumber(), Color.WHITE, no);

I have included a screenshot below showing how this plots on a chart. Notice that extended hours are NOT included on this chart. If you were to include extended hours on the chart then the code would also use that data in computing it's values.