Identify records where sales order contains multiple items

Here's a better explanation:

I have a recordset that looks like this:

Sales Order	Item ID	Accessory
ABC100	302	1A
ABC100	443	2A
EFG200	105	1A
EFG200	105	1B
HIJ300	790	3A

I need to identify the sales orders containing multiple (unique) items. Any ideas for a formula that could help me mark each of those records? Items will often appear more than once in this excel file because an item can be associated with multiple accessories. I would be looking for something like this:

Sales Order	Item ID	Accessory	Multiple?
ABC100	302	1A	Yes
ABC100	443	2A	Yes
EFG200	105	1A	No
EFG200	105	1B	No
HIJ300	790	3A	No

Thank you for your help.