'*** <shift-F5> to run, <Alt> f x n   to exit
CLS
COLOR 15
PRINT "Plot of `Leaky Tank' "
PRINT
INPUT "Initial level - 0 to 40 (try 0 first) "; x
INPUT "Input U, 0 to 20       (try 20 first) "; u

k = .5
dt = .01       'Edit to try various values of steplength dt

SCREEN 12
VIEW (1, 1)-(638, 328), 8, 12
WINDOW (-.5, 0)-(5.5, 40)

DO
   x = x + (-k * x + u) * dt      'This is the simulation
   t = t + dt
   PSET (t, x)                    'This displays the result as dots
LOOP UNTIL t > 5