We're dividing 399691 by 1 
The aim is to understand the frequency of 1 in 399691.

Step 1:
If we divide 3 by 1, we get 3 and a remainder of 0.
Put 3 as the next digit of the answer. 
Result so far: 3.0
If we take 3 away from 3, we end up with 0.
Append the next digit (9) from the dividend to 0 and continue with: 9 / 1

Going ahead to step 2:
1 goes into 9 9 times with a remainder of 0.
Put 9 as the next digit of the answer. 
Result so far: 39.0
Subtracting 9 from 9 leaves us with 0.
Include the next digit (9) from the dividend after 0, then repeat: 9 / 1

Advancing to step 3:
9 divided by 1 is 9 with a remainder of 0.
Write down 9 as next digit of the result. 
Result so far: 399.0
If we take 9 away from 9, we end up with 0.
Include the next digit (6) from the dividend after 0, then repeat: 6 / 1

Let's proceed to step 4:
1 can be fit into 6 6 times, resulting in a remainder of 0.
Put 6 as the next digit of the answer. 
Result so far: 3996.0
Subtracting 6 from 6 leaves us with 0.
Fetch the next digit (9) from the dividend, attach it to 0 and continue: 9 / 1

Step 5:
When dividing 9 by 1, we get 9 with a remainder of 0.
Put 9 as the next digit of the answer. 
Result so far: 39969.0
Subtract 9 from 9 to get 0.
Include the next digit (1) from the dividend after 0, then repeat: 1 / 1

On to step 6:
1 goes into 1 1 times with a remainder of 0.
The next digit of our result is 1. 
Result so far: 399691.0
Deduct 1 from 1 and we're left with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

On to step 7:
1 can be fit into 0 0 times, resulting in a remainder of 0.
Use 0 as the next digit of our solution. 
Result so far: 399691.0
If we take 0 away from 0, we end up with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

On to step 8:
The number 1 fits into 0 0 times, leaving a remainder of 0.
Write down 0 as next digit of the result. 
Result so far: 399691.0
If we subtract 0 from 0, we get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

The final outcome is 399691.0, with a leftover of 0.0.