patriot

patriot
  The Patriot missile system "ticked" every tenth of a second.
  It computed time in seconds as S = T * ONE_TENTH
  The system used 24 bit floating arithmetic.
  ONE_TENTH was stored as 0.099999905
  This meant that the computed time S differed from the
  real time R, and this error increased unless the system
  was rebooted.

  The Scud missile traveled at V=1,676 meters per second.
  A position error of more than 137 meters means the
  Patriot cannot intercept the Scud.

  Here is what gradually happens as the system stays on alert.

      h        t            r            s      r-s     v*(r-s)
  hours    ticks          sec          sec      sec      meters
                         true     computed    error  scud error

      0        0       0.0000       0.0000   0.0000         0.0
      1    36000    3600.0000    3599.9966   0.0034         5.7
      8   288000   28800.0000   28799.9726   0.0274        45.9
     24   864000   86400.0000   86399.9179   0.0821       137.6
     48  1728000  172800.0000  172799.8358   0.1642       275.1
     72  2592000  259200.0000  259199.7538   0.2462       412.7
     96  3456000  345600.0000  345599.6717   0.3283       550.3
diary of