Cartridge alignment tool

All these suggestions are good, but you should know one thing about the Mint - It requires you to line up the cantilever between two minuscule parallel lines and this is very painstaking and, IMO, virtually impossible on a cartridge with a small, tucked-in cantilever.  It's much better for carts like the Lyra with an out-front cantilever.  Just letting you know.  I bought one, but it was just too onerous with my Transfiguration cartridge. 
I just use the gauge that came with my Basis tonearm and it sounds fine.   

Though expensive, the Smartractor is the best. It saves a great deal of time, easy to use and has a unique alighnment called the UniDin (along with all the others). I love this alignment since you seem to get no perceptible IGD. I know it’s not inexpensive, but if you have multiple carts it saves you gobs of time. 

brf, thank you for your reponse, I think I would go for the MintLP, for my REGA RP6 / RB303 tone arm.  For the download printable protactor, it is the hole to make after the printing, that may cause errors ?

I agree fully with @last_lemming 
Nothing comes close to the Acoustical Systems Smartractor. For me, it is well worth the investment even if you only have 1 cartridge. I have typically only had 1 cartridge at a time except for the last few years when I have had 2 arms and 2 cartridges. It gets me the best result and that has made it invaluable to me.

audiosens,
If you go with the Mint be SURE to measure your pivot to spindle distance accurately.  In my experience if it's off by even 1 mm of the factory spec, the Mint arc will be off and it will be impossible to align both null points simultaneously.  I had incurable sibilance until I measured the P2S at 2 mm long and corrected it (previous table).  Mint used to custom make their protractor to your P2S spec if the arm wasn't adjustable.  That would be the way to go if need be.  It's a case of "close enough" will definitely not work.  It has to be spot on.Here are some Rega specific protractors and others.  
https://www.vinylengine.com/cartridge-alignment-protractors.shtml
Their Rega Stevenson protactor lines right up with the Rega factory one that came with my RP-10.  My P2S is 223 instead of 222.  I have to stick with the single null point protractors because the third screw mount for the Apheta 2 cartridge is not slotted and I can't quite reach the proper overhang.  I wonder if that screw is really necessary..