I'd keep track of the user-logins on a per-computer basis in a central location, then once a day aggregate the data.
Alternatively, and preferable, updates derectly into a database (MS Access has a 255 concurrent user limit and anything over 10 concurrent users is supposed to be very slow and prone to errors). Better use the free MSDA or open-source databases.
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There are two types of vessels, submarines and targets.
