A B737-700 WAS DISPATCHED IN NON COMPLIANCE WITH THE L MAIN GEAR SHOCK STRUT INCORRECTLY SVCED.

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ON THE AFTERNOON OF FEB/WED/02; I WAS CALLED BY ACR OPS AT ZZZ THAT ONE OF THEIR BOEING B737-700'S HAD WHAT APPEARED TO BE A LEAKING L MAIN LNDG GEAR SHOCK STRUT. THE COMPANY WHICH I WORK FOR PROVIDES 'ON CALL' CONTRACT MAINT TO SEVERAL COMMERCIAL AIRLINES. I DROVE OUT TO THE ACFT; CHKED WITH THE FLC AND VERIFIED THE DISCREPANCY HAD BEEN ENTERED IN THE ACFT LOGBOOK. I PROCEEDED TO INSPECT THE L MAIN LNDG GEAR STRUT. I FOUND THE STRUT TO HAVE NORMAL EXTENSION EQUAL TO R MAIN LNDG GEAR STRUT EXTENSION. THE STRUT WAS CLEAN WITH THE EXCEPTION OF A THICK BLACK STREAK OF DIRTY HYD FLUID ON THE BACK SIDE OF THE CHROMED AREA OF THE INNER STRUT. I WIPED OFF THE DIRT AND CLEANED THE CHROME AREA WITH A CLEAN RAG AND MIL-H-5606 HYD FLUID. I THEN REINSPECTED THE STRUT AND FOUND NO EVIDENCE OF LEAKAGE. I CALLED ACR MAINT CTL IN ZZZ1; AND INFORMED THEM OF THE LOGBOOK DISCREPANCY AND WHAT MY INSPECTION HAD DISCLOSED. ACR MAINT CTL REQUESTED THAT I PERFORM A NITROGEN SVC OF THE L MAIN LNDG GEAR 'PER THE STRUT SVCING PLACARD' LOCATED IN THE L WHEEL WELL; AFT BULKHEAD. I BROUGHT DOWN OUR COMPANY'S NITROGEN SVC CART AND PROCEEDED TO SVC THE L MAIN LNDG GEAR STRUT WITH NITROGEN. WHEN COMPLETED; I MEASURED THE STRUT EXTENSION AND COMPARED IT TO THE NITROGEN PRESSURE IN THE STRUT AND DETERMINED THAT THE PRESSURE AND EXTENSION FELL WITHIN THE SVCABLE BAND ON THE STRUT SVCING PLACARD. THE STRUT SEEMED TO HAVE MORE THAN NORMAL EXTENSION; APPROX 1 INCH MORE EXTENSION THAN THE R MAIN LNDG GEAR. I REVERIFIED THE PRESSURE VERSUS EXTENSION 3 TIMES AND EACH TIME FELL WITHIN THE SVCING BAND OF THE STRUT SVCING PLACARD. I THEN; PER THE DIRECTION OF ACR MAINT CTL; SIGNED OFF THE ACFT LOGBOOK 'INSPECTED L MAIN LNDG GEAR SHOCK STRUT. NO LEAKS NOTED. SVCED L MAIN LNDG GEAR STRUT WITH NITROGEN PER STRUT SVCING PLACARD LOCATED IN MAIN WHEEL WELL. OK FOR SVC. MAINT CTLR NOTIFIED.' THE ACFT THEN RETURNED TO SVC. I WAS BOTHERED BY WHAT I THOUGHT WAS EXCESSIVE STRUT EXTENSION AND SO LATER EXAMINED ANOTHER B737-700 MAIN LNDG GEAR SHOCK STRUT SVCING PLACARD. ON CLOSE EXAMINATION OF THE PLACARD; I REALIZED THAT I HAD NOT MEASURED STRUT EXTENSION FROM THE PROPER LOCATION. STRUT EXTENSION IS SUPPOSED TO BE MEASURED FROM THE BOTTOM OF THE GLAND NUT TO THE TOP OF THE AXLE. I HAD MEASURED THE STRUT EXTENSION FROM THE BOTTOM OF THE GLAND NUT TO THE BOTTOM OF THE CHROMED AREA ON THE INNER STRUT. THIS RESULTED IN APPROX 3/4 INCH ADDITIONAL STRUT EXTENSION. I IMMEDIATELY NOTIFIED ACR MAINT CTL IN ZZZ1 OF MY ERROR. A FOLLOW-UP CALL TO ACR MAINT CTL LATER THAT EVENING PROVIDED ME WITH THE FOLLOWING INFO: THE ACFT FLEW 1 LEG FROM ZZZ TO ZZZ1;. AT ZZZ1; ACR MECHS CHKED THE SHOCK STRUT AND FOUND 'NO LEAKAGE.' ACR MECHS DID FIND THE SHOCK STRUT SLIGHTLY OVEREXTENDED AND ADJUSTED STRUT EXTENSION TO THE PROPER DIMENSION. THE ACFT CONTINUED IN SVC. THE FOLLOWING FACTORS CONTRIBUTED TO MY IMPROPER SVCING OF THE SHOCK STRUT: MOST OF MY EXPERIENCE HAS BEEN ON THE EARLY MODEL 'CLASSIC' B737'S; 737-200; -300; -400; -500. THE STRUT SVCING PLACARD ON THESE ACFT SHOWS WHERE THE STRUT EXTENSION DIMENSION (X-DIMENSION) IS TO BE MEASURED ON A LARGE DIAGRAM ON THE PLACARD. THE B737-700 MAIN LNDG GEAR SVCING PLACARD SHOWS THE X-DIMENSION ON A MUCH SMALLER DIAGRAM ON THE PLACARD. LOOKING AT THE SMALLER DIAGRAM; I CONFUSED THE LOWER LINE OF THE X-DIMENSION WITH THE LINE REPRESENTING THE BOTTOM OF THE CHROMED AREA ON THE INNER STRUT. AS THE LOWER LINE FOR THE X-DIMENSION CORRESPONDS TO A POINT ON THE TOP OF THE AXLE AND IS APPROX 3/4 INCH BELOW THE CHROMED AREA OF THE INNER STRUT; I SVCED THE STRUT APPROX 3/4 INCH IN EXCESS OF THE PROPER STRUT EXTENSION.