Comma Interference How helpful commas are! They let you from a western country pronounce the numbers easier because the commas are added every three digits. 1,000 is one thousand, of course. 10,000 is ten thousands. 1,000,000 is one million. You also have an advantage to multiply on account of the commas. For instance, One thousand times one thousand equals one million. (1,000 X 1,000 = 1,000,000) Ten thousands times one thousand equals ten million. (10,000 X 1,000 = 10,000,000) One million times one thousand equals one billion. (1,000,000 X 1,000 = 1,000,000,000) Wow! amazing! That sounds like a magic. If commas were added every four digits to group like below, it would be much much easier for Japanese to pronouce them. 1,0000 is 1man. 10,0000 is 10man. 100,0000 is 100man. 1,0000,0000 is 1oku. 1,0000,0000,0000 is 1cho. But the reality is like below. 1oku = 100,000,000 10oku = 1,000,000,000 Have you already realize that Japanese need a bit longer time to realize how large the number with commas is? Because they ignore(!!) the commas and count all of the digits from right to left like "ichi, ju, hyaku, sen, man, ju-man, hyaku-man, sen-man, ichi-oku, ah, this is 1oku." Moreover, most of Japanese haven't noticed the similar mutiplying like I told above because of commas. For instance, 1man X 1man = 1oku 10,000 X 10,000 = 100,000,000 (every three digits) 1,0000 X 1,0000 = 1,0000,0000 (if every four digits) 10man X 1man = 10oku 100,000 X 10,000 = 1,000,000,000 (every three digits) 10,0000 X 1,0000 = 10,0000,0000 (if every four digits) 1oku X 1man = 1cho 100,000,000 X 10,000= 1,0000,0000,0000 (every three digits) 1,0000,0000 X 1,0000= 1,0000,0000,0000 (if every four digits) The convenient commas added every three digits make multiplying inconvenient in Japan. I think it can be called Comma Interference.