It should be remembered that when the rubber platen of a billing machine becomes worn and cut with holes incident to the use of periods, commas, hyphens, etc., the special character type will sometimes print heavy at the top and light at the bottom of the letter, or _vice versâ_. This is remedied to some extent by placing a new rubber roll on a cylinder billing machine, or a new rubber covering on a flat-bed billing machine. Special characters are used to a better advantage on the under-stroke (or blind machine) than on the visible machine. In the latter, the type-bars are all grouped in less than a half circle, which necessarily crowds the type-bars a little closer together, and therefore does not permit of special characters of a large size. =Tabulators on Billing Machines.= It is absolutely essential that every billing machine be furnished with either a single-stop (known as a _column-stop_) tabulator or a decimal tabulator, preferably the latter. A single-stop tabulator is used as follows: On the billing machine frame rests a bar on which metal stops or pegs are placed at predetermined intervals. By pressing the column stop, the carriage holding the paper is released, and jumps automatically to the first stop. After the information is written, the stop is again pressed, and the machine jumps automatically to the next printing point. The following example shows the use of the column stop: John Jones Marion, Ind. XXV A. B. Smith Washington, D. C. XXX G. Barnes Seattle, Wash. XXX The following example shows the use of the decimal tabulator: 10.50 .50 150.25 15560.65