# Setting Probes If you wish to see the state of data at a given chain point, right click the chain point and select **New probe…**

The following dialog box appears:

To set a probe, you can specify CSV lists of variables and values that must be matched *(or you can leave the fields blank to have the probe trigger on the next transaction through that chain point).* Variable can be surrounded by various special characters to indicate additional criteria. For example, consider a variable named VAR: * `VAR` : means that VAR is equal to the selection value (exact match) * `!VAR` : means that VAR is not equal to the selection value * `VAR*` : means that the VAR content starts with the selection value * `*VAR` : means that the VAR content ends with the selection value * `*VAR*` : means that the VAR content contains the selection value * `VAR<` : means that the VAR content is less than the selection value * `VAR>` : means that the VAR content is greater than the selection value For the `<` and `>` characters, the value will first be attempted to convert to a number. If that succeeds, numeric comparisons are performed. If not, a lexical comparison will take place. **Tip:** the value field is matched literally. Setting variable `VAR` with the value left blank only matches transactions where VAR is itself empty. To match *any* value of VAR (i.e. trigger whenever the variable is present), use `*VAR*` with the value left blank: the contains-match treats an empty target as always present. You can also select the occurrence number of the probe to see. This is especially useful when debugging loops. By default, only the first 100 characters of any variable is recorded. Once the probe is set, the chain point changes color to yellow:

It will stay yellow until a matching transaction reaches the chain point, at which point it will turn red:

You can now see the variables as they were when they reached the probe. To do this, right click on the chain point again and select **View probe**:

A dialog box appears with the variable information:

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