This has been covered many many times on the forum so why not one more time...

Basically we want multiply the ADC value by 135/1023=0.132 so in comes the */ operator.... 0.132*256=34 (rounded up).

1023*34/256=135
512*34/256=68
128*34/256=17

When the value you want to multiply by is <1 you can get more precision with the ** operator (same thing but inherent division by 65536). In this case it doesn't matter though because the output value range is so small.

Do note that there's no expensive division going on here, all it does is discard the bottom 8 bits (in the case of */) of the multiplication.

/Henrik.