# Difference between “Level” and “Flow” in the Z.1 Fed data

The Z.1 Fed data can be found in FRED.

I notices that many similar data sets are labelled "Flow" or "Level". For example,

And sometimes, the Level version for a Flow series doesn't exist or vice verse.

What is the difference?

Now suppose you decide to subtract the levels that correspond to year $$t-1$$ from the levels that correspond to year $$t$$. That's what the Fed is doing with these data series -- the flows are the first-difference of the levels.