TRIO 3-IN-1 ANALGESIA SYSTEMGet three test systems in one package with the Trio, featuring the Electronic von Frey, Plethysmometer and Randall Selitto meters. Just like the Quattro package, the modular design allows these three test systems to communicate with the same electronic controller. The stand and sling for the Randall Selitto test are sold separately. Three test systems Electronic von Frey Plethysmometer Randall Selitto