how can i convert the close for today to a constant value that I can use in other calculations? I don't want to use code like x = close() because then x would vary each day.

@TrickyDick

You can try the following. It is assigned to the first Close bar.

 

Code

double todayClose = 0; // initialized in OnStartup() // In OnBarUpdate() if( todayClose == 0 ) todayClose = Close[0]; // Assigned once only

Thank you for responding, but I don't understand your answer for two reasons.
I pasted your code into a new ThinkOrSwim study, and the study rejected almost every line.
(1) TOS doesn't accept the word double. I tried double.NAN and other things but TOS still doesn't accept it.
(2) I think you're using '//' as a remark, but TOS requires '#' to show remarks
I changed '//' to '#' but then the script was still rejected because of (1) is an invalid statement

Would you please provide more information.
Thank you.