  We consider the problem of minimizing resources required for universal
quantum computation using only projective measurements. The resources we focus
on are observables, which describe projective measurements, and ancillary
qubits. We show that the set of observables {Z \otimes X, (cos\theta)X +
(sin\theta)Y all \theta \in [0, 2\pi)} with one ancillary qubit is universal
for quantum computation. The set is simpler than a previous one in the sense
that one-qubit projective measurements described by the observables in the set
are ones only in the (X,Y) plane of the Bloch sphere. The proof of the
universality immediately implies a simple set of observables that is
approximately universal for quantum computation. Moreover, the proof implies a
simple set of observables for preparing graph states efficiently.
