Power query - determine conditional difference

I've loaded a .csv file which contains data from 4 sensors. Example below: the .csv data I've loaded using Powerquery consists of 3 columns "Time", "Source" and "Value". I aim to get the changes in the "Values" column to a new column called "Delta", using Powerquery. I have not been very successful so far. How to do this?

Time Source Value Delta
00:00 Sensor A 150 150
00:00 Sensor B 20 20
00:00 Sensor C 50 50
00:00 Sensor D 80 80
00:05 Sensor A 120 -30
00:05 Sensor B 25 5
00:05 Sensor C 60 10
00:05 Sensor D 90 10
00:10 Sensor A 100 -20
00:10 Sensor B 40 15
00:10 Sensor C 60 0
00:10 Sensor D 105 15

*bumperty-bump*