NavList:

I am new at this so be patient. Before retiring my work was precise with hand tools. This comment is based on those experiences it may also be something you already do that I am not aware of. The pictures I see though do not show different though.

When I hold my sextant I try to do it in a way to minimize as much bobbing around by having my muscles working in unison. First I use my left eye to center the sextant between my shoulders  for balance and uniform tension between my shoulders and tension on the sextant. The second thing I have done is make a eye piece that fits on the sight tube or telescope out of silicon that fits on my eye socket to stabilize the sextant on my face, it also blocks light glare.

These are just things that help my accuracy. Would be interested in feed back from you with more experience   thanks