We look at the division of 1975491 by 643 
The aim is to understand the frequency of 643 in 1975491.

Step 1:
If we divide 1 by 643, we get 0 and a remainder of 1.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we subtract 0 from 1, we get 1.
Bring next digit (9) of the dividend behind the 1 and repeat the process: 19 / 643

Moving on to step 2:
The number 643 fits into 19 0 times, leaving a remainder of 19.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 19, we end up with 19.
Take the next digit (7) from the dividend and append it to 19, then repeat: 197 / 643

Moving on to step 3:
643 goes into 197 0 times with a remainder of 197.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we subtract 0 from 197, we get 197.
Fetch the next digit (5) from the dividend, attach it to 197 and continue: 1975 / 643

On to step 4:
The number 643 fits into 1975 3 times, leaving a remainder of 46.
The next digit of our result is 3. 
Result so far: 3.0
Subtract 1929 from 1975 to get 46.
Fetch the next digit (4) from the dividend, attach it to 46 and continue: 464 / 643

Step 5:
When dividing 464 by 643, we get 0 with a remainder of 464.
Use 0 as the next digit of our solution. 
Result so far: 30.0
If we take 0 away from 464, we end up with 464.
Append the next digit (9) from the dividend to 464 and continue with: 4649 / 643

Moving on to step 6:
If we divide 4649 by 643, we get 7 and a remainder of 148.
The number 7 becomes the next digit in our result. 
Result so far: 307.0
Subtracting 4501 from 4649 leaves us with 148.
Include the next digit (1) from the dividend after 148, then repeat: 1481 / 643

Advancing to step 7:
The number 643 fits into 1481 2 times, leaving a remainder of 195.
The next digit of our result is 2. 
Result so far: 3072.0
If we take 1286 away from 1481, we end up with 195.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1950, and continue the process.

Step 8:
643 goes into 1950 3 times with a remainder of 21.
The number 3 becomes the next digit in our result. 
Result so far: 3072.3
Subtracting 1929 from 1950 leaves us with 21.
Since there are no more digits in the dividend, we add a zero to the remainder making it 210, and continue the process.

Let's proceed to step 9:
643 goes into 210 0 times with a remainder of 210.
Record the quotient 0 as the next digit in the result. 
Result so far: 3072.3
Subtracting 0 from 210 leaves us with 210.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2100, and continue the process.

Moving on to step 10:
When dividing 2100 by 643, we get 3 with a remainder of 171.
Record the quotient 3 as the next digit in the result. 
Result so far: 3072.303
Subtract 1929 from 2100 to get 171.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1710, and continue the process.

Moving on to step 11:
643 can be fit into 1710 2 times, resulting in a remainder of 424.
Record the quotient 2 as the next digit in the result. 
Result so far: 3072.3032
The remainder is 424 after subtracting 1286 from 1710.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4240, and continue the process.

Step 12:
When dividing 4240 by 643, we get 6 with a remainder of 382.
Put 6 as the next digit of the answer. 
Result so far: 3072.30326
The remainder is 382 after subtracting 3858 from 4240.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3820, and continue the process.

Moving on to step 13:
If we divide 3820 by 643, we get 5 and a remainder of 605.
Write down 5 as next digit of the result. 
Result so far: 3072.303265
Deduct 3215 from 3820 and we're left with 605.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6050, and continue the process.

Let's proceed to step 14:
643 can be fit into 6050 9 times, resulting in a remainder of 263.
Put 9 as the next digit of the answer. 
Result so far: 3072.3032659
If we subtract 5787 from 6050, we get 263.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2630, and continue the process.

Moving on to step 15:
If we divide 2630 by 643, we get 4 and a remainder of 58.
Use 4 as the next digit of our solution. 
Result so far: 3072.30326594
If we subtract 2572 from 2630, we get 58.
Since there are no more digits in the dividend, we add a zero to the remainder making it 580, and continue the process.

The final outcome is 3072.30326594, with a leftover of 5.8e-08.