VISIBILITY RPT FIRST IN MI; THEN RVR CONFUSED FLC AND ACFT LANDED BELOW VISIBILITY MINIMUMS.

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WHILE ON FINAL TO SAN 27 LOC RVR WAS CALLED AT 5500-4500 FT. OUR CHARTS SHOW ONLY VISIBILITY REQUIREMENTS OF 1 3/4; NOT RVR. TWR CALLED VISIBILITY AT 2 MI. WE HAVE NO REF TO GUIDE US ON WHETHER WE COULD USE MI OR RVR ON APCH. WE DID NOT HAVE TIME OR FUEL TO GO MISSED APCH WHILE WE LOOKED UP APPROPRIATE CONVERSION AND COULD NOT FIND ANY GUIDANCE AFTER WE LANDED. WE WERE GIVEN WX OF 800 FT BROKEN 2 RAIN SHOWERS. BEFORE WE WERE ON THE FINAL APCH SEGMENT; THE ACFT AHEAD OF US WAS GIVEN RVR OF 5500 FT. OUR PLATES SHOW REQUIRED VISIBILITY OF 1 3/4 MI; WITH NO RVR VALUE GIVEN. THE APCH; IN HARD RAIN; IS BAD ENOUGH; REQUIRING 2 PLTS' FULL ATTN TO FLY THE PROFILE FOR A SAFE APCH AND LNDG. WE HAD NO TIME TO LOOK UP LEGALITIES WHEN A CONFLICTING VISIBILITY VALUE IS GIVEN. LOOKING BACK; WE SHOULD HAVE MISSED AND DIVERTED FOR SEVERAL REASONS. BY ITS DEFINITION; RVR TOP VALUE IS 6000 FT; WHICH IS LESS THAN 1 3/4 MI. SO; IF ANY RVR IS GIVEN; AND IF IT IS INDEED CTLING; VISIBILITY IS LESS THAN THE CAT C APCH MINIMUMS. I RECOMMEND THAT AN F-4 BE ADDED TO SAN FLT PLANS CLARIFYING THAT IF THE TWR GIVES AN RVR VALUE FOR THE LOC 27 APCH; IT IS BELOW OUR MINIMUMS AUTOMATICALLY. I FURTHER RECOMMEND THAT PART 1 HAVE SOME FIRM GUIDANCE TO COVER OUT SIT.