If just used for AT, then 4240 is ok. It's an "entry" level display so it's not able to do a lot of the mid to higher level functions of the 4640. It's a bit smaller, slower processor, less features/functions. But if you just need it to steer it'll do that. (as long as the machine you're putting it in is compatible)
Difference between 4240 and 4640
