yes, the mikrokator is extremely sensitive. but the needle always trembling doesnt really help. well, maybe im trying to do something that cant be done with my equipment. thats why i asked. e.g., i put two parallels on the stand together and when i come in from one side one of them is higher, when i come in from the other side the other one is higher. in both instances the plunger has to come up from the gap to the surface, so im clueless. its clearly not a random error. and i have rotated the parallels to exclude any irregularities of the plate.
On the experience, you are looking in the wrong place. What is CARRYING your indicator so as to "come in from" a choice of more than one direction of approach to "static" work? Same equation and same question if the DI is "fixed" to a spindle or head or bridge and it IS the work, on a slide table, doing the moving to "come in from".
If a lathe or mill traverse? THOSE -
and/or their lubes - just "do not" slide exactly the same way, both directions. See also surface grinders and "surfing".
At least - not down at the uber-fine measure you seek to utilize.
If it is the height gadgetry being slid atop a surface plate on its base-buttons, it is STILL not "immune" to variances in handling or the environment.
Have a "clean room"? Dust particles you cannot even SEE or feel may as well be a graveled road at these units of measure.
Working with BARE HANDS? The human body outer layer is DEAD skin cells, constantly renewed from new ones growing under it.
Good system. Keeps us from bleeding out or having to slither about all wet - like pond scum. It ALSO dumps an outrageous aount of dead skin cell debris, all the time, and WORSE just after a shower or bath.
Try your approach at a dead-slow crippled snail's rate of movement. With pauses to settle. You may see a change? Pick the one it is most predictable and repeatable with. Use that one, going forward. Else correct from a log of consistent errors, by chosen direction.
"And then...."
In general, a(ny) machine-tool's variances are GREATER, and not my just a little bit, than any hysteresis in the metrology gear of that fine-grain a class as you are applying.
SIP and Moore addressed such things. Tier One grinder makers as well. Few others played in the same league, then or now, that ordinary mortals could
afford to purchase.
Message there is that if/as/when you get THIS part "dead nuts repeatable", you still have to go and do something USEFUL with it in the less-perfect arena.