Calculate the difference across two attributes

Hey guys, I got a metric endpoint which posts a history value and keep suming up.

Was wondering how can I define a simple NRQL query to calculate the difference between the two timestamps.

For example if the latest value is 100 and 30 minutes ago was 90, I need to calculate the diffence and plot just the diffence on the chart.

Something like a TIMESTAMPDIFF {fn TIMESTAMPDIFF(30 minago,60mingo)}

SELECT latest(status_total) FROM Metric - latest(status_total) SINCE 30 MINUTES AGO FACET Name, status TIMESERIES