Soft-I/O supports counting and timing functions that allow you to do many common control functions.  Let's look at a few.

Counting: Counting pulses is often useful when dealing with flowmeters.  Many flow meters employ some kind of spinning element whose rotation is detected with a magnetic Hall sensor or simply a photo sensor looking for holes or slots in the rotating piece.  In flow meters, flow is almost always proportional to counts produced.  So, 1,000 counts might be 1 liter.  If we count the pulses, we can totalize the flow.

Setting up a Soft-I/O counter could not be easier.  You simply  name the counter Soft-Device, for example, "Total Fuel Pumped".  Since you want to count and not time, you need to associate the counter with another Soft-Device that is putting out pulses.  In this case, it's the fuel flow sensor input, often configured as a proximity sensor, either two- or three-wire.  Don't forget to turn off the debounce filter on the input since Soft-I/O is so fast, that it will double- or tripple-detect switch closures.  As a result, the default debounce time for a Soft-I/O switch-type input is 30 milliseconds.  Set it to zero.  Now, simply use the Count Source Soft-Device drop down menue in the counter Soft-Device and select your flow sensor.  Most of the time, you'll want to count up, but the counter will alow count down.  Hit the submit button and you are done!  Go to the Soft-Device page and watch the counts accumulate as you run your flow meter.  If you want flow rate, look at the excellent Soft-I/O Rate Soft-Device.  It's more advanced than any PLC or DCS and will give you an excellent signal.

Timing: To do timing, you will use the Timer Soft-Device.  The timer has a lot of built in flexibility.  It can be set up to be free-running or to run/reset.  If you are timing an event, you would probably use the free-running mode.  If, however, you are building a watchdog timer, then the run/reset mode is what you want.  You can configure a sequence to act when the terminal count occurs, indicating that your watchdog has expired.

Summary: If you wanted this kind of functionality in a PLC or DCS system, you would buy some type of timer or counter module.  You would then wire it up, program it and probably have a solution that is less flexible than the Soft-I/O solution.  With Soft-I/O, there is only one part number!  You simply select the Soft-Device you need from a list of included Soft-Devices in the module.  You "wire" it up by dragging and dropping on your web browser.  What could be simpler?