Sometimes it would be useful to be able to compare two variable values in your filter steps.
For example, imagine you're taking orders on your website via a form. To keep things simple, you sell just one product. You want to trigger a zap that compares the number of pieces of that product the customer wants with your available stock (which you track via a Google Sheet) and only send an order confirmation email if you've got enough stock.
When the zap triggers, one of the fields will be the quantity ordered. Your next step will be a Google Sheets lookup and one of the fields returned will be quantity of stock left.
Next you need to add a Zapier Filter that only continues if the ordered quantity is less than stock quantity. But these are two variables and this doesn't seem to be possible with Zapier.
In fact, it is if you follow the stepps described in the video below.