Display timestamp difference between two values in same serie

I have a time serie like GasSummaryConsumption.
I would like to construct a expression / query to display virtual value of timestamp difference between two one after the other values.
How should be expression/query builded please ?
Like ?
select ELAPSED(“value”) FROM “GasSum”
displays dif in nanoseconds.
How to convert it to minutes, seconds please ?
Overide in ns displays correct in mins.
Raspbian,Influxdb 1.8

Assuming you are using InfluxQL (and not Flux), the elapsed() function should work. You just need to change the unit to minutes, as specified in the documentation, e.g.

> SELECT ELAPSED("value",1m) FROM....

Thanks for help.
Is this query staement correct for display the GasSum as dots without line interpretation ?
SELECT ELAPSED(“value”,1m) FROM “GasSum” FILL(null)

Looks correct to me.