How to do symbolics like 2.5*in+9*ft--->XX*mm+YY*mm

Can redefine units as a variable, suggest changing name though:

The symbolic processor knows nothing about Mathcad's built-in units. The symbolic processor treats them as undefined variables, just like any other undefined variable. You can play around with defining the units yourself, as Wayne suggests, or you can play around with substitute, but that's all. I can't comment on why substitute didn't do what you want because you didn't post a worksheet. You also created this as a document rather than a discussion thread, so nobody else can post worksheets either.

Hi Richard,

As you can see from the above picture, I can only get the final result 2806.7mm, but can't get what I wanted XX*mm+YY*mm=2806.7mm

Hi Wayne,

Thanks for you idea, I have another question below.

Don't think you have any control, Mathcad is going to use the base unit m.  The had to choose, and that's what they choose.

It seems the reason is not about the base unit m. See below.

The symbolic processor does not understand units. It just sees mm as an undefined variable, like any other undefined variable.

Thanks for you idea, I have another question below.

Because of the inline evaluaton it sees "m" attached to the IN and FT values. It sees "m", which is what is stored internally, regardless of what you type in the unit placeholders in the inline evaluations. And to the symbolic processor, "m" is just another undefined variable.

Thanks