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: 
According to the [docs](https://help.salesforce.com/apex/HTViewHelpDoc?id=customize_functions_i_z.htm&language=en_US#ISCHANGED)

> 
> ISCHANGED function returns FALSE when evaluating any field on a newly created record.
> 
> 
> 

So your validation will never fire when you are creating a record. You might want to add `ISNEW()` function which checks if you are creating a new record.

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

```
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)))

```