One main scale division of a vernier caliper is equal to $m$ units. If $\mathrm { n } ^ { \text {th } }$ division of main scale coincides with $( n + 1 ) ^ { \text {th } }$ division of vernier scale, the least count of the vernier caliper is :\\
(1) $\frac { n } { ( n + 1 ) }$\\
(2) $\frac { 1 } { ( n + 1 ) }$\\
(3) $\frac { m } { ( n + 1 ) }$\\
(4) $\frac { m } { n ( n + 1 ) }$