True statement regarding "tuberculine test" is -

The tuberculin test is the only means of estimating the prevalence of infection in a population . Produce a pale wheal of the skin, 6 to 10 mm in diameter. The result of the test is read after48-98 hrs but 72 hrs(3rd day) is the ideal. Reaction exceeding 10 mm are considered positive. Ref:PARK&;S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE 23rd edition , Page 185