10 step exposeure calculator. 

A4 in size.

you will need some thick light proof apper or card or even some ruby film.

tape calculator to screen.

guesitmate your exposure time(or ask us) and then double it..(if you think its 5min, then we start at 10min)

so because its a 10 step calculator, we cover numbers from 1 to 9 with that card/ruby and expose that for 1min, them move it along to cover 1-8 and expsoe for another 1min, then 1-7 tand expose and  1-6 and so on and on.

when finished, number 10 will have got 10min of light, and number 1 will only get 1min of light.

wash out like a normal exposure.

then figure out which is the best exposed number...easy.