Hi. There are four discount buttons available on this model. Do you know which it is? It will usually show %1, %2,%3, or %4 when you use it.
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If anyone needs more information, the Samsung / Sam4s ER-4940 manual is here:
http://the-checkout-tech.com/manuals/cashregisters/Samsung_ER-4940_dealer_pocket_programming_guide_manual.html
Registerman
March 2011