Calculates the diameter of inside rim of a roll of material on two rims. The required dimensions are as given in the table. Variations due to stretching or softness of the material are to be ignored. The length units that can be used are yard, feet, inch, meter, centimeter, millimeter and mil. A mil is equal to one thousandth of an inch. The initial units used in the table can be changed to any of the choices given. Please take note that the distance between the inside rims refers to the distance between the centers of the rims.