Can you please find the logic of Marco's calculator bug?

Question

Marco is a mathematician. He has a calculator that can solve problems.
Unfortunately, his calculator is infected by a bug.

He dared to try some math problems but now the equations look like this:

21 + 30 = 18
192 - 63 = 2
49 - 12 = 3
234 + 653 = 30

What is the logic of this bug?

Hint: The name of this bug is Seven Segment.

Answer 1

Counting number of segments for each given digit as per picture: e.g 21=5+2=7, 30=5+6=11

---

---

21 + 30 = 18 --> 7 + 11 = 18
192 - 63 = 2 --> 13 - 11 = 2
234 + 653 = 30 --> 14 + 16 = 30
49 - 12 = 3 --> 10 - 7 = 3