float delta;
float sizeToStart;

// Example values
delta = 15.0;
sizeToStart = 50.0;

if (brushSize <= delta+sizeToStart ) {
precision = 5;
} else if (brushSize > (delta + sizeToStart) && brushSize <= (delta*3)+sizeToStart) {
precision = 4;
} else if (brushSize > (delta*2)+sizeToStart && brushSize <= (delta*4)+sizeToStart ) {
precision = 3;
} else if (brushSize > (delta*3)+sizeToStart && brushSize <= (delta*5)+sizeToStart ) {
precision = 2;
} else if (brushSize > (delta*4)+sizeToStart ) {
precision = 1;
}