Well first point is both of these are great cash registers. Both have some very strong points to be made for them. Not really fair to compare however because the Sharp ER-A420 has been around a long time before some of the newest features of the SAM4s SPS-320 was being used in the industry.
Both cash registers feature a large flat keyboard. The SAM4s keyboard is a little large. Both can interface to credit card payments with the Datacap Twin Tran, both can interface to PC Poll cash register software.
the Sharp ER-A420 has a history of being incredibly durable and is a heavy duty machine for sure. The SAM4s line up as a whole has a great track record of being reliable.
Couple huge advantages of the SAM4s SPS-320 include the SD card port for program back up and flash ROM upgrades, free software and the eight line LCD display.
If I already had the Sharp ER-A420 I would stick with them for a while since you would have no learning curve with operations, if starting with a cash register for the first time go with the SAM4s.
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