A restricted area may be closed for all purposes, open to transit, open to fishing for a specific period, or open to designated vessels only. Vessel speed is often the way its status is determined in lieu of direct observation. Some VMS directly report speed, or speed can be calculated by FMS software based on the time stamps of different position reports. A rule of thumb in scallop fisheries, for example, is that the vessel cannot be dredging for scallops if its speed is greater than .