This works but it's a bit of a hack (i.e. I don't know how/if you can have the label the same side Appearance-&gt;"Labelled" would put it):

Manipulate[
 a = Round[k, .1];
 Plot[Cos[k x], {x, 0, 2 Pi}], {{k, 1, Dynamic@a}, 0, 
  SetPrecision[4.0, 22], SetPrecision[0.100, 22]}]


How to set precision and format labeled Slider in Manipulate?
Note that the only measure of location in nominal variable is mode.

Is there also any measure of variance?
Obviously, some nominal features are more different than other (color of eyes vs. presence of some rare disease).
