How many different production codes are there for the episode with 4.69 million US viewers?
CREATE TABLE "table1_26429543_1" (
  "no_in_series" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" real,
  "u_s_viewers_millions" text
);
SELECT COUNT("production_code") FROM "table1_26429543_1" WHERE "u_s_viewers_millions"='4.69';