We put in the assumption that the average client makes 10 such requests per day. A tor client that is connected 24/7 makes about 15 requests per day, but not all clients are connected 24/7, so we picked the number 10 for the average client. Dividiamo semplicemente le richieste di directory per 10 e consideriamo il risultato come numero di utenti. Another way of looking at it, is that we assume that each request represents a client that stays online for one tenth of a day, so 2 hours and 24 minutes.