MyRewards

The new McDonald's MyRewards app, and associated MyRewards program, allows you to have special coupons deals or rewards.  Accessing this program is done by QR codes, but the QR codes very often do not work.  The readers on the McDonald's kiosks seem to be pretty much useless in terms of scanning the offers.  The readers at the tills do a much better job. 

The app does allow you to access coupons and rewards at the kiosks, by entering a code.  The code, used both for rewards and for coupons, and for identifying yourself to the system in order to build rewards, are all accomplished using four digit numbers.  This is interesting since it allows 10,000 possible combinations.  I assume that the coupons must be time limited, but, since using the app with the kiosk does involve several delays, one assumes that the time out, must be longer than a minute.  Let's propose five minutes.  In fact let's propose six minutes, since that makes the math a little bit easier. 

Allowing for six minutes means that there are 240 possible periods in a day.  Given the four digit codes, this allows for slightly under two and a half million possible orders per day.  In fact, the total number would be somewhat less than that, since you would not want to use the entire address space, and, in any case, you would not be able to evenly distribute the orders over the entire day.  Some periods of the day would be much busier.  Five in the afternoon would be a much busier time than 3:00 in the morning. So the total number of orders would be much less efficient than the theoretical limit.

Allowing for an incomplete use of the total address space, in order to prevent people simply guessing at login numbers, and allowing for the inefficiencies of random entry of orders, and slower periods of the day, it's unlikely that you would get more than 200,000 orders per day.  This is rather interesting.  It may be that this is spread worldwide, or it may be that the MyRewards program is limited to North America.  Even so it's interesting that the system is limited in this manner to such a small apparent ability to generate orders, given the promotion that the app and the program are being given by McDonald's. 

Of course I assume that the system itself is not hard coded for a four digit number.  The coupon codes may be extended and complicated with letters and numbers in the future to accommodate a much larger address space.