What's the duration of the period? Previous day's high and low?
Here is an example for your watchlist column:
	
	
	
	
	
		
Set the timeframe of the column to D (daily).
	
		
			
		
		
	
				
			Here is an example for your watchlist column:
		Ruby:
	
	def prev_high = high[1];
def prev_low = low[1];
plot value = prev_high - prev_low;
	Set the timeframe of the column to D (daily).