This is percentage change in open interest between 2 subsequent trading days. Suppose the open interest (OI) position on Monday is 100 and on Tuesday is 120, 1 day change in OI is calculated as (120/100) – 1*100 = 20%. A positive output indicates rising number of OI’s whereas a negative output indicates drop in OI’s. 

As a rule of thumb, if the spot price of the stock and OI of futures both move up, it indicates a bullish signal and prices might continue to rise. A decrease in price with an increase in OI or conversely an increase in price with a fall in OI both indicates a bearish signal.