Google Latitude on multple devices

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I have Google Latitude on my Galaxy S1 phone and on my Android tablet. Some of my friends also have it their phones and Android tablets. When I look for their locations, I see that it is incorrect, as for example, I see that my sons location is at home, when he is actually at work. On asking, seems that his tablet is at home, and his phone is with him. So, how does Latitude distinguish? Is there a way to only update location of phone and ignore the tablet?
Thanks

BTW I'm a newbie here, so apologies if I have mistakenly asked an available question