The manual method

An obsolete method for the conversion of n to N scores consists of incrementing the number of matchpoints by 1 for every missing score, i.e.
SN0  =  Sn + N - n

Sn = the number of matchpoints from a normal calculation with n scores
SN0 = the resulting increased number of matchpoints.
We express this in percentages Pn en PN0, and multiply left and right by 100, obtaining:
(2N - 2) PN0  =  (2n - 2) Pn + 100 ( N - n)

PN0  =   (Pn − 50) · n−1

N −1
 + 50

Compared to Neuberg

PN  =  (Pn − 50) · n−1

· N

N −1
 + 50
a factor of N/n is missing from the difference with 50. The method pulls the scores too close to 50% and this effect is larger the more N/n is larger.

A simple example:
a fouled board where 7 scores are to be split in two groups, of 3 and 4 scores, respectively.
According to this method the top with 3 scores is 66.7% and with 4 scores 75%.
With Neuberg we would have found: top with 3 scores 88.9% and with 4 scores 93.8%.

That is quite a difference. It is even better to proportionally stretch the scores to a top of 100%, than to use this method.

Before the advent of the computer this method was generally used. As we see, mistakenly.