Having been derived from the Hindu numerals, modern Khmer numerals also represent a decimal positional notation system. It is the script with the first extant material evidence of zero as a numerical figure, dating its use back to the seventh century, two centuries before its certain use in India. However, Old Khmer, or Angkorian Khmer, also possessed separate symbols for the numbers 10, 20, and 100. Each multiple of 20 or 100 would require an additional stroke over the character, so the number 47 was constructed using the 20 symbol with an additional upper stroke, followed by the symbol for number 7. This inconsistency with its decimal system suggests that spoken Angkorian Khmer used a vigesimal (based on units of twenty) system.