Calculating my personal tax code

I am trying to understand how my tax code is calculated. I have a personal allowance of 12700 and a state pension of 10500 so my tax free amount is 12570-11500 or 1070. A recent notice about the tax code says in Note 4: "To create your tax code we have removed the last digit or your tax free amount and added a letter". So why is my tax code 108, not 107? Talking to a friend, they too have a discrepancy of 10. What else is in the calculation, or is this an extra, early, Christmas bonus?

Hi GSB,
There may be additional allowances present in your code, or the deduction from your state pension may be slightly lower than 11,500.
If you would like us to review your code, please contact us by webchat or phone here:
Income Tax: general enquiries
Thank you.