This is from a T1N service manual
STANDARD PROCEDURE
STANDARD PROCEDURE - INJECTOR
CLASSIFICATION
The classification of injectors into 3 classes
describes the quantity characteristic of the injector.
This will make it possible in the future to match the
engine software to the tolerances of the injector
within a more narrowly graduated range. Classification
can be clearly recognized, and assigned only by
means of a DRBIIIt.
Classified injectors can be recognized by the part
number and identification on the magnetic head (circle
with a number between 1 and 3 inside) (Fig. 9).
The number corresponds to the classification stage.
These general conditions equally apply if, as a
result of replacing an engine, carrying out repairs to
the cylinder head etc., the cylinder selective assignment
of the injectors or the engine control module
assignment may have changed. If proper attention is
not paid to the classification on these vehicles driveability
and smoking concerns could result.
If an injector is replaced, it is then necessary to
assign the classification number to the corresponding
cylinder with the DRBIIIt in the control module.
INJECTOR CLASSIFICATION PROCEDURE
(1) Turn ignition switch “ON”.
(2) Using a DRB IIIt and select ENGINE then
MISCELLANEOUS.
(3) Select LEARN INJECTORS.
(4) Using the up and down arrows, scroll to the
appropriate injector.
(5) Using the right and left arrows, set injector to
proper classification.
(6) Once injectors are classified, cycle ignition to
complete.