How many type classifications are given to the measure with the description, calling convention to revise state constitution? 
CREATE TABLE "1910_general_election" (
  "meas_num" real,
  "passed" text,
  "yes_votes" real,
  "no_votes" real,
  "pct_yes" text,
  "const_amd" text,
  "type" text,
  "description" text
);
SELECT COUNT("type") FROM "1910_general_election" WHERE "description"='Calling Convention to revise State Constitution';