Spin frequency distribution. The red bars represent 10 nuclear powered pulsars whose spin frequency is measured via burst oscillations during thermonuclear bursts. The 13 accretion powered pulsars are identified by blue bars, and no accreting pulsar with spin below 100 Hz is counted in the sample, according to the definition of millisecond pulsar. Note that the red and the blue histograms are not overlapped, but they are added. If a pulsar is both accretion powered and nuclear powered, I have counted it as an accretion powered. The total number of neutron stars in the sample (accretion plus nuclear powered) is 23.