  Explicit formulas for the rotation frequency and the long-wavenumber
diffusion coefficients of global spirals with $m$ arms in Rayleigh-Benard
convection are obtained. Global spirals and parallel rolls share exactly the
same Eckhaus, zigzag and skewed-varicose instability boundaries. Global spirals
seem not to have a characteristic frequency $\omega_m$ or a typical size $R_m$,
but their product $\omega_m R_m$ is a constant under given experimental
conditions. The ratio $R_i/R_j$ of the radii of any two dislocations ($R_i$,
$R_j$) inside a multi-armed spiral is also predicted to be constant. Some of
these results have been tested by our numerical work.
