I've told you about this before:

Because the watt is named after Mr Watt, the symbol is a capital 'W';

Because the hertz is named after Mr Hertz, the symbol has a capital 'H';

The lowercase multiplier 'k' means 1000 (10³);

The uppercase multiplier 'K' means 1024 (2 ¹⁰)

http://www.8052.com/forum/read.phtml?id=29676

Please write this out 1000 times as your weekend homework! ;-)