  We have calculated the linear magnetoconductance across a vertical parabolic
Quantum Dot with a magnetic field in the direction of the current. Gate voltage
and magnetic field are tuned at the degeneracy point between the occupancies
N=2 and N=3, close to the Singlet-Triplet transition for N=2. We find that the
conductance is enhanced prior to the transition by nearby crossings of the
levels of the 3 particle dot. Immediately after it is depressed by roughly 1/3,
as long as the total spin S of the 3 electron ground state doesn't change from
S=1/2 to S=3/2, due to spin selection rule.
  At low temperature this dip is very sharp, but the peak is recovered by
increasing the temperature.
