# A specific value cannot be present elsewhere
This rule is used to determine if a value **does not exist** elsewhere, it is more advanced than the [Item must not have been entered elsewhere](/blocworx-documentation/bloc-editor/managing-a-field/field-rules/item-must-not-have-been-entered-elsewhere.md), because it uses a second value as a reference to look up the data.\
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For example, in a manufacturing test environment, a unit may have to have failed an initial first test in a different bloc in order to be repaired. So in this case the serial number of the unit is checked, and the value we are checking is "Passed". The rule would fail if "Passed" was the result.
### Rule Parameters
| Parameter | Description |
| ---------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Bloc to Look Up | The Bloc to check against. (Note, the "Type Module or Job Name" field is not a rule parameter and is simply used for finding blocs in your instance.) |
| Reference Field to Look Up | The field inside the bloc you have selected. This field is the one you are using as your lookup, for example, we want to look up a serial number field in a different bloc. |
| Field to Check Value against | The field we want for comparing values, in our example, if we need a serial number to have failed somewhere, this field may be something like "Test Result" |
| Value it cannot be equal | This is the value that the "Field to Check Value Against" cannot equal. So sticking to our example, this might have the word "Passed" where "Field to Check Value Against" or Test Result cant equal "Passed". If it does the rule fails as we are trying to make sure the unit has **not** passed. |
| Exception Field to Look Up | We may have exceptions to the above criteria, and for this reason we may want to ignore certain entries that have other data in them. An example of this being used might be that the unit did in fact passed but perhaps ones that have a comment added them to them still need to be reworked. This option allows you to pick the field to check this. |
| Exception Values | This only applies if "Exception Field to Look Up" is selected. Here we determine the values where the exception can be applied. So, a full scenario might be:
- We find this unit and it does have the Test Result : Passed
- This should normally break the rule, but we might have an exception field called "Ignore" and exception value "True", and if that entry has that same data then the rule does not break.
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