  We constructed a transportable 40Ca+ optical clock (with an estimated minimum
systematic shift uncertainty of 1.3*10^(-17) and a stability of
5*10^(-15)/sqrt{tau} ) that can operate outside the laboratory. We transported
it from the Innovation Academy for Precision Measurement Science and
Technology, Chinese Academy of Sciences, Wuhan to the National Institute of
Metrology, Beijing. The absolute frequency of the 729 nm clock transition was
measured for up to 35 days by tracing its frequency to the second of
International System of Units. Some improvements were implemented in the
measurement process, such as the increased effective up-time of 91.3 % of the
40Ca+ optical clock over a 35-day-period, the reduced statistical uncertainty
of the comparison between the optical clock and hydrogen maser, and the use of
longer measurement times to reduce the uncertainty of the frequency
traceability link. The absolute frequency measurement of the 40Ca+ optical
clock yielded a value of 411042129776400.26 (13) Hz with an uncertainty of
3.2*10^(-16), which is reduced by a factor of 1.7 compared with our previous
results. As a result of the increase in the operating rate of the optical
clock, the accuracy of 35 days of absolute frequency measurement can be
comparable to the best results of different institutions in the world based on
different optical frequency measurements.
