I guess the 82 store you bought from is out of stock, so take the 81 and put one with the 82 label on it. You can connect the water to the maximum water level and pour it into a graduated cylinder to measure it. Next, the maximum capacity of 81 is 1100ML, and the maximum capacity of 82 is 1300ML. There is still a big price difference between the two. If you buy 82 and turn it into 81, you will suffer a loss.