mint block of four (positions 24-25, 34-35), the "8 cts." surcharge is from positions 23-24, 33-34 as the overprint was shifted horizontally, therefore the right two stamps do not exhibit the 3mm spacing between "8" and "cts." variety (20.6) as one would normally expect on the fifth vertical row, very fine and rare, these stamps originate from the same pane that produced the "8 cts." double error (20d), a full explanation can be found in the Canal Zone Philatelist Vol. 38, No. 3