Author: Ricardo Gibert
Date: 16:52:18 09/08/02
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On September 07, 2002 at 11:13:20, Robert Hyatt wrote: > >Jose made a really good point about observed data vs measured data. After >thinking about it for a bit, I decided that it is a point strong enough to >change the way we think about "measured" and "observed". > >Some examples: > >speed. Impossible to measure. > >For example, your automobile (newer vehicles) compute speed by counting the >revolutions of the tailshaft (output) of the transmission, then factoring in >the rear-end ratio and the circumference of the rear wheels. It _computes_ >the speed from that. > >A radar measures the frequency change in a radio signal as it bounces off >a moving target and _computes_ the speed based on the frequency change. > >A GPS observes to "positions" in terms of lattitude and longitude, uses some >geometry to compute the distance between them, and uses a clock to measure the >time to cover that distance, and displays speed. > >So Speed can't be measured directly, it has to be computed. And this isn't a >surprise since speed is defined as distance over time. > >Brightness. (of a light, not a person. :) ) > >This is a direct measure of an electrical signal produced by some sort of >device (photo-resistor, photo-cell, optical transistor, etc) and then that >voltage is used to compute a brightness level in Lumens... > >Loudness (sound). > >Ditto. > >NPS. > >nodes searched divided by time in seconds. Computed. > >Speedup > >one-processor time divided by the N-processor time. Computed > >We really don't have a lot of "observed" data nowadays. Some, yes. Where >were you at 8pm last night. But more is computed... > >Which means if we start to define observed vs computed, we don't end up with >very much in the "observed" column. > >In a chess program I can count nodes and "compute" time (end-time minus >start-time) and then compute a nps value. I can measure run-time and compute >speed-up. But I can't directly measure speed at all. > >strange when you think about it... :) You have to compute run_time too: run_time = completion_time - start_time ;-)
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