1  = loop on 1 (finger) 
2  = loop on 2
5  = loop on 5
1a  = Heart side of 1
1b  = World side of 1
2a  = Heart side of 2
2b  = World side of 2
5a  = Heart side of 5
5b  = World side of 5
R before string designation = right; (i.e., R1 = right loop on 1(finger))
L before string designation = left; (i.e., L1a = left "heart side of 1 "on 1(finger))

Ref. 1) isfa Nomenclature (n:near side; f:far side, instead of a,b designation on strings)
Ref. 2) Eric Lee's Notation (same to isfa on strings)