Convert Base26 to Base10

Base26ToBase10.cs

// Our example symbol
var symbol = "ABC-1234";

// Use a lookup to avoid calling Math.Pow in a code hot path
int[] Base26Pow = { 1, 26, 676 };

// Get the first 3 digits of our symbol
var base26 = symbol.AsSpan(0, 3);

var base10 = 0;

for (int i=0; i < 3; i++)
{
  // Iterate through each digit, derive its value from 
  // its ASCII code and multiply by its Base26 position
  base10 += (base26[i] - 64) * Base26Pow[3 - (i + 1)];
}