Today's PSA

Uncertain Principles: The Delete Key Is Your Friend

Look, people: the delete key is your friend. There is no need to send every bit of the exchange on to new people. If you’re only responding to the most recent email, do us all a favor and delete the rest of the quoted text. If you’re forwarding something on to a new audience, delete everything but the most essential part of the message. We don’t need to see all the deliberation that went into the decision to forward: just send the key message.

This is especially important when you use a free email system that tacks on twenty or more lines of crap at the end of the email, and all you’ve added is “LOL.”

Homo sapiens

Homo sapiens

Zoo visitors and staff have been surprised by the addition of a new and unexpected enclosure at Bristol Zoo Gardens.

A mysterious sign has appeared on the side of the Zoo’s popular Coral Café, designating the area as a place to spot one of the world’s most widespread species – Homo sapiens.

The notice, which appeared without warning this week, shows humans ‘on display’ inside the café and includes tongue-in-cheek description of the species and its characteristics.

My Turf

Built onFacts: Time and Navigation

Matt gives a brief summary of time and navigation. There’s one point that he glosses over, and it’s something that a lot of GPS summaries gloss over, to the point that they are misleading.

All a GPS satellite does is eternally broadcast two continuously updated pieces of information: its position and the time on its atomic clock. Knowing that light travels at about 1 foot per nanosecond, we can calculate how far we are from the satellite to the foot, as long as the GPS clock is accurate to the nanosecond and we have a receiver that can handle such a precise signal.

Actually you can’t do this unless you have a synchronized clock, and unless you’ve done this already, in order to synchronize the clocks properly you have to know … [wait for it] … the distance to the satellite. Many of the explanations of GPS completely miss this little tidbit. If you haven’t got a synchronized clock, and all you have are the GPS signals, you need four satellites to find your position. In practice four may not be necessary, because if you know your approximate position on the earth and have a topographic map, you can get the elevation from that, in which case three satellites is sufficient to get your position, to some level of uncertainty.