Find tickmarks for a given range of the y-axis that best fit an optimal number of tickmarks you decide. f.i: what if i want to have a graph with 8 tickmarks in a range of 34 to 345
optimal.tickmarks( i.min, i.max, i.number.ticks = 10, i.valid.ticks = apply(expand.grid(c(1, 2, 2.5, 5), 10^(-10:10)), 1, FUN = function(x) { x[1] * x[2] }), i.include.min = F, i.include.max = F )