p1,m1,f1

These variables specify the field in the input record for the numeric test.

p1 specifies the first byte of the field relative to the beginning of the input record ¹. The first data byte of a fixed-length record (FLR) has relative position 1. The first data byte of a variable-length (VLR) record has relative position 5 (because the first 4 bytes contain the record descriptor word). All fields must start on a byte boundary, and no field can extend beyond byte 32752.
m1 specifies the length of the field. The length can be 1 to 256 bytes.
f1 specifies the type of numerics the field is to be tested for as follows:
FS

test for numerics in character format ('0'-'9' (X'F0'-X'F9') in all bytes).
Note: CSF can be used instead of FS.

ZD

test for numerics in zoned decimal format ('0'-'9' (X'F0'-X'F9') in all non-sign bytes; X'F0'-X'F9', X'D0'-X'D9' or X'C0'-X'C9' in the sign byte)

PD

test for numerics in packed decimal format (0-9 for all digits; F, D or C for the sign).

You can use p1,m1 rather than p1,m1,f1, if you use FORMAT=f to supply the format for the field.