The gauge and length of the needle would be used.
The tuberculin is administered with a single-dose disposable needle that has a quarter to half inch needle.
The ruler line should be placed on the inside left edge of the induration.The ruler line should be read on the inside right edge of the induration.Reading should not be recorded as positive or negative.Only record the measurement in millimetres.If there is no induration, record as little as possible.
After 30 days, discard the tuberculin vial.If you store tuberculin with other vials, they could be mistaken for it.Do not pre-fill the tuberculin before administering TST.