I want to change the increments on the line spacing tool so that when I use the + and - buttons, the line spacing changes only by a few pixels.  Thanks.

The units of the line spacing tool can be changed using the text controls bar:

Thanks for the info.  I was wondering, though, if there were a way to change how many "units" or "increments" it would change by when you click the up/down arrows.  For example if the units are pixels, I want it to change by only .5 of a pixel every time I click the up/down arrows instead of a full pixel.  

What version of Inkscape and what OS are being used?

In my Inkscape 1.01 on Linux, the line spacing increments in tenths.

Inkscape 0.92 (I reverted back from 1.01) and Windows 10.  It is a full pixel change instead with each.

I understand. I'm using .92 here for most tasks.

I'm experimenting with adding another unit to the units.xml file that has a factor of 0.5 (px) to get half pixel increments. But there is something buggy about the GUI and nonstandard units... the appear, but the GUI won't keep them in the selected units and reverts back to whole px. 😕

.5 px would be fantastic!