this is only useful when you head down to HKJC betting shops and you only have your shitty cellphone calculator.

any odds above 2 are pretty easy...just subtract 1 times 100 and add a plus sign to the front.

for any odds from 1 to 2, all you have to do is to calc 100/decimal part and then times a 100 and add a minus sign to the front.

for example 1.62 -> 100/62 = 1.61, so it is -161. this is easy because all you have to type into your cellphone calculator is 100/61...or 1/61...that is only about 4-6 key strokes.