Time velocity value STAAD is not matching with manual calculation

STAAD SS6 20.07.11.90 Version is used 

I have created STAAD file with Single RPM (355)

If we see the max displacement value obtained in this STAAD is 7.51 E-3 mm = 0.00751 mm

 

Now using standard equation to calculate Velocity

Velocity = ω x Dmax = 2 π f Dmax = 2π x (355/60) x 0.00751 = 0.279 mm/sec

But in STAAD value given is 299 E-6 mm/sec. So there is huge difference in manual (0.279mm/sec) and STAAD calculated values (299 E-6 mm/sec). 

Would you please enlighten me how to compare STAAD value with manual calculation and also let me know if my manual calculation is right or wrong?

Regards,

Hemant.