ES;

stands for the extreme spread of the shots fired in a test.

Ten is normal but some of us cheap skates go with 4-5 shots
to save bullets and get a "Ruff" estimate of what a load does....

with maybe more tests later if the load is promising..... ?
Right now I am working on the 38 special 130gr HST out of a snub nose J frame.

It can or can't help a shooter......
I shot for 40 years without a chrony and it did not hurt my shooting.

Just more data to give you gray hairs.