There IS a way to calculate demand without markets and money though. For example, let's say that we can calculate demand by tracking purchases of items. Basically, imagine it like this; 10,000 people go to a superstore. They pick out the items they want/need and then go to a checkout counter at the front of the store. At this checkout counter, they are required to place all their items on the counter, and the items are electronically scanned and given back to the customer. At the end of the day, the list of which items are sold and how many are posted to a government website, where businesses and anyone else can see the exact demand for each item. This is just my own idea of how demand would be calculated in Communism.