Exact Etch length

Hi Guys,

 i need to make a cline an exact length for RF purposes how can i do this while routing manually.

im using Allegro PCB designer 16.5. i have tried setting the Min Total etch length to 31.339mm and the Max to 31.339mm.

the trace also needs to be a curve. 

Also i was just wondering how come quick reports-> etch length by net. does not include the pad length?

Regards