**nfast**: Number of barotropic timesteps needed to compute time-averaged barotropic variables centered at time level n+1

**ndtfast**: Number of barotropic timesteps between each baroclinic timestep.

I am confused with the time-stepping in ROMS.

For example, I set

**dt**= 150s,

**ndtfast**= 30 in

*ocean.in*, so I got

**dtfast**= 5s, and I also got

**nfast**= 42 computed by

*set_weights.F*. In

*main3d.F*, there are 42 barotropic time-steps for each

**dt**, rather than 30 steps. SO my question is that are there 12 time steps(M*-M) double counted for each

**dt**? For the next baroclinic step n+2, the barotropic step starts from m=M or from m=M* on the figure attached?

Could anyone give me a further explain? Thank you very much!