Question: Hi i got a requirement like create a validation rule based on probability.

The requirement is user cannot modify some custom field called forecast units If probability is under 70%

So, i write a validation rule like 

```
AND(ISCHANGED( Forecast_Units__c ),Probability < 0.70)

```

It works fine but when i create any opportunity the validation doesn't work
can anyone help me

Answer: 
That is because the validation will only fire on the field being changed. To make it work on creation you would need to use ISNEW

So I think the following will work updated based on Adrian's input and checking that Forecast\_Units\_\_c is populated. 

```
 AND(Probability < .7, 
    OR(AND(ISNEW(),NOT(ISBLANK( Forecast_Units__c ))), 
       ISCHANGED(Forecast_Units__c)))

```
**EDIT:** This validation below is incorrect, the only thing you can learn from it is how to *DO NOT USE* a combination of `ISNEW()` and `ISCHANGED()` formulas in Validation Rules ))

```
AND(
 NOT( ISNEW()),
 ISCHANGED( Forecast_Units__c ),
 Probability < 0.70
)

```

Would allow you to bypass this validation when new record is created.