Premarket 50% line

For this solution we are going to barrow some code provided in a previous request: https://www.hahn-tech.com/ans/premarket-study-on-chart/

That previous post links back to another so be sure to follow the links to get the full context. The original post you find will be a request for a premarket High/Low label. This code gives us all the structure we need to add in the 50% line. Be sure to read those previous posts so that you understand how to use this code:

input startTime = 400;
input endTime = 929;
input percentLevel = 0.5;
def timeUntilClose = SecondsTillTime(endTime);
def timeUntilOpen = SecondsTillTime(startTime);
def targetPeriod = timeUntilClose > 0;
rec targetPeriodHigh = if targetPeriod and !targetPeriod[1] then high else if targetPeriod and high > targetPeriodHigh[1] then high else targetPeriodHigh[1];
rec targetPeriodLow = if targetPeriod and !targetPeriod[1] then low else if targetPeriod and low < targetPeriodLow[1] and low > 0 then low else targetPeriodLow[1];
def pmHigh = targetPeriodHigh;
plot fiftyPercentLine = ((pmHigh - close(period = AggregationPeriod.DAY)[1]) * percentLevel) + close(period = AggregationPeriod.DAY)[1];

Screenshot below shows the result. Note that the previous day close and premarket high lines have been drawn on the chart by hand. This code only plots the 50% line.