Use Probes to check intermediate values on a wire as a VI runs. Use the Probe tool if you have a complicated block diagram with a series of operations, any one of which might return incorrect data. Use the Probe tool with execution highlighting, single-stepping, and breakpoints to determine if and where data is incorrect. If data is available, the probe immediately updates and displays the data during execution highlighting, single-stepping, or when you pause at a breakpoint. When execution pauses at a node because of single-stepping or a breakpoint, you also can probe the wire that just executed to see the value that flowed through that wire.
- "Using the Probe Tool" by National Instruments (http://zone.ni.com/reference/en-XX/help/371361R-01/lvhowto/using_the_probe_tool/)