Cutting up a rear axle.

What numbers are you asking about.

If it's the tube length number, that's the length from insertion point at the center section to flange. Take those two tube length numbers and add 17.5" to it. The total should equal the housing number above just below the blue cell.

You really need to know how long you want the rear end in total, put that number into the blue cell and it will give you the total housing length, tube lengths and axle lengths.

If you go to the wheel offset tab, mess around there. It will get you close depending on wheel width, minitub or not, springs moved or not... It's not perfect, but will get you an idea.

Best to get your wheels and tires, center them in wells and measure.