tickStep function
Calculates the step size for tick generation.
Implementation
double tickStep(double start, double stop, int count) {
if (count <= 0) return 0;
final step0 = (stop - start).abs() / count;
var step1 = math.pow(10, (math.log(step0) / math.ln10).floor());
final error = step0 / step1;
if (error >= _e10) {
step1 *= 10;
} else if (error >= _e5) {
step1 *= 5;
} else if (error >= _e2) {
step1 *= 2;
}
return stop < start ? -step1.toDouble() : step1.toDouble();
}