The applet above simulates a queuing situation. It starts with a newly opened service, with no one being served or waiting. Once you start the simulation, each arrival or completion of service is indicated in large print. The display is updated once each second.

Lambda and Mu can be changed by changing the numbers in their boxes. Press Enter while the cursor is in one of the boxes to effect the change.

The numbers below the big box allow you to see what the random number generator is doing. Each second, new random numbers between 0 and 1 are generated.
If the first number is less than lambda/60, there is an arrival. The left box turns green.
If the second number is less than mu/60, there is a service completion. The right box turns pink. (Unfortunately, not all browsers display these colors properly.)

Click on the Reset button to restart from 0.