Compare values from now and 2 hours ago and how the difference


As can be see from the chart below we have a sensor that is recording pressure. The pressure has dropped 2 points within 2 hours. If this drops 2 points within 2 hours, this causes us some problems. I would like to create a query that compares the values from now and 2 hours in the past and display the difference. How can i achieve this in influx query language?