4.21. STOCK AND FLOW DIAGRAM WITH VENSIM
A simulation model with Vensim
A soldier stopped in front of a clock shop every day at 8 o'clock in the morning and adjusted his watch comparing it with the chronometer situated in the window display. One day the soldier went into the shop and congratulated the owner on the exactness of the chronometer.
"Are you in line with time from Westminster?" asked the soldier.
"No" answered the owner "I adjust it according to the canon fire at 5 o'clock in the castle. "why do you stop here everyday and check the time of your watch?"
The soldier answered, "I am the one who fires the canon".
Knowing that the chronometer from the clock shop is delayed about one minute every 24 hours, and the clock of the soldier is delayed 1 minute every 8 hours, What is the total error in the time of the canon in the castle after 15 days?
To introduce this scheme into the computer we have to translate it to the format of the flow diagram. This model presents the particularity that the time is the variable Level. We have to differentiate the real time (24 hour/day, 1440 minutes) from the time measured by clocks, this being something almost physical that we can manipulate.
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