Delta calculations

Den_er_da_hvid

I have a dataset with hourly observations the last three years og different water meters. 

The issue is that the observations shows the meter stand, and not the water usage. 

I want to calculate/show a delta change for each hour, for each water meter. How do I approach that? 

Some of the analysis I want to make with this dataset is to find if a meter has a negative usage at one point (indicating water running the wrong way) or that a meter has to big a delta indicating a leakage.

My workplace is starting to work on data quality, so besides the above I will also want to look at things like if timestamps are consistent or if there is change in the timestamps (if observations for a specific meter is not comming back at the same minut-number each hour). 

One analysis tool I am looking forward to explore is the process quality