The voting machines are not connected to the internet, so nobody can change the result from outside, Central Election Commission (CIK) spokeswoman Stoyanka Balova told Bulgarian National Television (BNT).
Every receipt from the machines will carry a 30-digit hash code. The commission will generate it next week and make it public.
Balova said voters will be able to use the code to check that the machines run the certified software. They only need to remember the first and last four digits.
Earlier this week, commission staff showed people in the Sofia metro how to vote with a machine. The commission said people have asked for more demonstrations. Balova said some people still do not know how to vote with a machine, and some came specially to try it.
Anyone can practise voting with the "Izbori 360°" mobile app.