I am sure one of the clever guys will be along to give a definitive answer, however logic would say that the entry dialog is looking for a value to feed into just such a variable as you want to use. So you need a numeric value.
Have you tried copy / paste using the measure tool? You can copy/paste (ctrl-c/ctrl-v) from one dialog to the other.
of course you can also copy/paste from tool options as well for more regular shape selections.
Have you tried copy / paste using the measure tool? You can copy/paste (ctrl-c/ctrl-v) from one dialog to the other.
of course you can also copy/paste from tool options as well for more regular shape selections.