Answering the latest request on UGEARS Facebook page. Hope it will be interesting to you as well
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What’s is the combination of plugs in the discs of Safe model for the wanted code 426?
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Let’s suppose you would like to put the code 426:
A=4, B=2, C=6
The Formula for setting plugs in the discs:
a) P2 = P3 – ((B – A + 8) mod 10)
b) P1 = P2 + (B – C) mod 10
where A, B and C are the digits of the wanted code.
For technical reasons, C can only be 1, 2, 6 or 7
P1, P2, P3 – plugs in the discs. For technical reasons, P3 – P2 ≠ 4
E.g. let’s find P1, P2, P3 for the wanted code 426:
1.
Complete formula a) step by step:
P2 = P3 – ((B – A + 8) mod 10)
P2 = P3 – ((2 – 4 + 8) mod 10)
P2 = P3 – (6 mod 10)
P2 = P3 – 6
If you don’t now ‘mod 10’, than just go to Google an type ‘6 mod 10’ and Google will tell you that it’s 6
2.
Set in valid values, there are many possible solutions. Just choose one with P2 and P3 being 0 to 9
P2 = P3 – 6
with P3 = 6, P2 is 0
with P3 = 7, P2 is 1
with P3 = 8, P2 is 2
with P3 = 9, P2 is 3
3.
Solve formula b) with the first of the possible combinations
We will use P3: 6 and P2: 0
P1 = (P2 + B – C) mod 10
P1 = (0 + 2 – 6) mod 10
P1 = -4 mod 10
P1 = 6
again: Google will tell you, that “-4 mod 10” is 6, just don’t think about what this means 
Solve formula b) with the second of the possible combinations:
We will use P3: 7 and P2: 1
P1 = (P2 + B – C) mod 10
P1 = (1 + 2 – 6) mod 10
P1 = -3 mod 10
P1 = 7
again: Google will tell you, that -3 mod 10 is 7, just don’t think about what this means 
Solve formula b) with the third of the possible combinations:
We will use P3: 8 and P2: 2
P1 = (P2 + B – C) mod 10
P1 = (2 + 2 – 6) mod 10
P1 = -2 mod 10
P1 = 8
again: Google will tell you, that -2 mod 10 is 8, just don’t think about what this means 
Solve formula b) with the last of the possible combinations:
We will use P3: 9 and P2: 3
P1 = (P2 + B – C) mod 10
P1 = (3 + 2 – 6) mod 10
P1 = -1 mod 10
P1 = 9
again: Google will tell you, that -1 mod 10 is 9, just don’t think about what this means 
So: for 426, use 606 or 717 or 828 or 939 for plugs in the discs.
At last, make sure to set the parts together with the right way – as told in the manual. See is important when the wheels are put into the safe (For technical reasons, C can only be 1, 2, 6 or 7)