On the One ...

"...show the count..."
"...in this way..."

If I just do 'short line' 'long line' for each number based on it's digit value and assign zero to 'short' and one to 'long', then we get this:

7.4.13
long, short, long
1 0 1

101 binary = 5 Hex, 5 Oct, 5 Decimal and as Decimal 5, it then is E in Alphabet.
Source: Me at the Windows calculator toggling between the settings to see which is what.


"How then could we make a code that can correct errors? One simple example is to repeat the message three times." ***

I put 101 'next' to itself three times...

101101101 in binary = 365 in decimal. Like 365 days a year maybe? Co-ink-e-dink!~

"...show the count of the 7, 4 and 13. In this way..." ***

7 x 4 x 13 = 364 (3+6+4) = 13

101101100 bin = 364 decimal.
101101101 bin = 365 decimal.

764 included as 1913 as 9113~@~6113 <~that way as 3116