The hold back function not working with units

[anon21378091]

I have the following

dp = Quantity[1, "pascal per millimeter"]
R = Quantity[10, "millimeters"]
\[Mu] = Quantity[1, "millipascal second"]
v[z_] := N[1/(4 \[Mu]) (dp)*(z^2 - R^2), 2]

But then getting

In[69]:= v[3 mm]

Out[69]= (9.0 mm^2 + 
   Quantity[-1.0*10^2, ("Millimeters")^2]) (Quantity[25., 1/(
   "Centimeters" "Seconds")])

This is not what I expecrted. I expectred a clean result in terms of mm/sec. What I did wrong?

[arnoudb (Arnoud Buzing)]

Did you try it like this:

v[Quantity[3, "mm"]]

This gives me:

-2.3*10^4 mm/s

Or with the CTRL-= method (press and hold Control key and press =):

v[ CTRL-= 3mm ]