TAPPI T 414 om-12:2012 Edition

This method measures the force perpendicular to the plane of the
paper required to tear multiple plies through a specified distance
after the tear has been started using an Elmendorf-type tearing
tester. It does not measure edge-tear resistance. The measured
results may be used to calculate the approximate tearing resistance
of a single sheet. It is not suitable for single-ply tear
testing. 

For highly directional boards and papers, prepare specimens
according to T 496 "Specimen Preparation for Cross Directional
Internal Tearing Resistance for Paper, Paperboard and Related
Materials." See section 8.5. 

Caution is recommended in interpreting results from weakly
bonded sheets, especially those containing lightly refined
long-fibered chemical pulps. The low rate of tear when multiple
plies are torn simultaneously may produce erroneously high results
(1).