I've written an example that does what you want without hardware. If you run the example you will see that the waveform chart will hold at 5 only when reading1 is above 5 AND reading2 is below 5. Go ahead and change reading1 and reading2 manually while the program is running and you'll get the idea. You will need to add the VIs to read from your hardware and you will be set. I hope this helps.
Regards,
Todd D.
Applications Engineer
National Instruments