Auto-Increment Change Orders

I have a column [Entry Type] which contains (Task, Change, Other). I use a web form to allow others to enter change orders. I would like to automate naming these change orders as Change Order 1, Change Order 2, Change Order 3, etc. 

I can use =COUNTIF([Entry Type]:[Entry Type],"Change") to obtain the number of change orders entered. How can I automate a column entry to auto-increment only change orders?

Adding or subtracting one doesn't suffice as it changes all entries. I believe it needs to take into account the created date or an auto-number column that could be referenced.

Thanks in advance,

Charles