Calculated Value - inconsistent units

[MartinGTE]

I am trying to create a calculated value and I am stuck with inconsistent values.
I have foundation thickness parameter which is a length and I want to minus a parameter which is a number.

Yet this is causing an inconsistent unit error.  Surly there is a work around.  Mind had gone totally blank.

[ToanDN · Accepted solution]

Thickness/1 - Number param

[MartinGTE]

Thanks, I was about to post saying I had worked it out.