In the score motor is running to score multiple of some point value, hitting one of those targets won't score what it normally would, until the motor stops.

Easy way to envision this:

You hit, say, a 100 point target, and the "100 POINT RELAY" is activated, once, to score the points (the "^" is the pulse to the relay):

TIME --->
-------------------^-------------------------------------

Now, you hit a 500 point target, and it starts the score motor to pulse that same relay 5 times in succession:

TIME --->
------------^-----^-----^-----^-----^-----------------

Now, imagine hitting another 100 point target, during (say) the 2nd of the 5 pulses:

TIME --->
------------^-----^-----^-----^-----^-----------------

-------------------^-------------------------------------

The relay is just "on" or "off" - it can't tell that it's being activated by two different switches at the same time. The 100 point hit just gets "swallowed" by the 500 point activity. So, the lights "blink" to indicate that _more_ points won't be scored until the motor run is completed.

If you've ever worked on an EM where there's a coil next to the coin acceptors that kicks in and out as the score motor runs, it's the same issue - the coil prevents coins from being accepted while the motor is running, when they might not register as credits.

Cool - thanks for the link.