fft – How can I calculate the output frequency steps of the rpmfreqmap function in matlab

The rpmfreqmap function in matlab has an input option resfor frequency resolution. With the output there is also a frequency resolution option res. If I specify a frequency resolution of 1 Hz:

[map,freq,rpmOut,time,res]=rpmfreqmap(randn(1,100000),3000,linspace(1,100,100000),1,'OverlapPercent',0);

With this the result will be res=1; as expected. But the frequency vector is freq(1:4)=[0 0.6665 1.3330 1.9996]. I would have expected freq(1:4)=[0 1 2 3].

Equally with no overlap I would expect the time vector to be time(1:4)=[0.5 1.5 2.5 3.5], but it is time(1:4)=[0.7502 2.2505 3.7508 5.2512]. So the relationship between frequency and time steps is delta_time=1/delta_freq, but it doesn’t align with the specification in res.

So, how can I derive the frequency step size of the output vector of rpmfreqmap?