510 Subfield $c - Location within source:

Subfield $c contains the specific location of the citation or reference within the source (e.g., page number, item number, etc.). Note that the first indicator position contains value 4 (Location in source given) when subfield $c is present.

Examples:

510 4#$aGoff,$cA-970

510 4#$aBM XV cent.,$cII, p. 346 (IB.5874)

510 4#$aSchramm,$cv. 4, p. 10, 50, and iii

510 4#$aLC Treasure maps (2nd ed.),$c13