In a screw gauge pick up the correct statement(s)

Options

A. Positive error exists when the head scasle's zeroth division is above the base line of the pitch scale, when the two studs are in contach.
B. Positive error exists, when the head scales zeroth division is below the base line of pitch scale, when the two studs are in contact.
C. Negative error exists, the head scale's zeroth division is above the base line of the pitch scale, when the two studs, are in contact.
D. Negative error exists, the head scale's zeroth division is below the base line of the pitch scale, when the two studs are in contact

Answer

A, D