CREATE TABLE table_840 ("Game" FLOAT, "Date" TEXT, "Team" TEXT, "Score" TEXT, "High points" TEXT, "High rebounds" TEXT, "High assists" TEXT, "Location Attendance" TEXT, "Record" TEXT)

How many different values if the number is high rebounds can be found for the game on March 13?
SELECT COUNT("High rebounds") FROM table_840 WHERE "Date" = 'March 13'
SELECT COUNT("High rebounds") FROM "table_840" WHERE "Date" = 'March 13'