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Use the Probe tool 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 during 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.

You can create a custom probe, use supplied probes, or use an indicator to view the probed data. You also can use a LabVIEW MathScript probe to view the data in a script in a MathScript Node as a VI runs.

Complete the following steps to use the Probe tool.

1. (Optional) If you want a probe to display the data that flowed through the wire at the last VI execution, use the Retain Wire Values option on the block diagram.
2. Right-click a wire and select Probe from the shortcut menu or select Custom Probe and a probe from the shortcut menu. A floating Probe window appears. If you have not yet selected a supplied probe or created a custom probe, LabVIEW searches the labview\vi.lib\_probes\default and the labview\user.lib\_probes\default directory and finds a probe that matches the data type of the wire you right-clicked. After you select a custom or default probe, it becomes the default probe for that data type. LabVIEW numbers the Probe window automatically and displays the same number in a glyph on the wire you clicked. You must run the VI to display data in the Probe window.
   
   You also can use the Probe tool to click a wire to display the Probe window.
3. Place more probes on other wires and objects in the VI where you expect the data to change. Move the Probe window out of the way if necessary.
4. Run the VI. The Probe window displays data passed along the wire.
5. Compare the data that appears in the Probe window to what you expected.
6. Close the Probe window to remove the probe. Probes close automatically when you close the block diagram.

You cannot use the Probe window to change data. The probe has no effect on the way a VI runs, aside from custom probes optionally acting as breakpoints.

Note  If you want to provide help to users about how to use the custom probe, do not place a Help button on the probe because LabVIEW only executes probes when data flows through the wire. Instead, you can provide help by adding text to the front panel of the probe or by adding description and tip information to each front panel control. To provide help for the entire probe, consider placing the controls on a tab control or in a cluster and adding description and tip information for the tab control or cluster.

There are three options available on the shortcut menu that appears when you right-click a Probe window that displays data:

• Find Wire—Finds the associated wire. LabVIEW brings the block diagram that contains that wire to the front and highlights the wire.
• Reinitialize to Default—Resets the value the Probe window displays to its default value.
• Copy Data—Copies the data for pasting to other controls in the same VI or in other VIs.