[Elecraft] Spot Function Question

[KD3TB]

With a new K3S, when I use the SPOT Function (in CWT) to tune in on a strong
CW signal, it makes a variety of Frequency changes depending upon how many
Hz digits are the VFO (settings)

 

For example:

When the VFO is set to 21.025.979  it goes to 21.026.018 a change in .039 Hz
a perfectly tuned in Signal

When the VFO is set to a few number of Hz digits in the display -  21.025.9
it goes to 21.026.8  (21.026.879) which is actually a change of 0.979 Hz and
a lost signal.  

 

I am using a strong signal and a 400 Hz filter. 

 

Since the display (number of Hz shown) should not have any effect on the
function of the spot,  what other settings to I need to look at?  

 

Thanks, Irwin - KD3TB