And a fundamental difference is a difference in some natural feature of the writing, indicative of the individual's writing habit that cannot be reasonably explained.A signature comparison is the identification of signatures and involves a combination of line quality and letter design.
The quality refers to things such as the paper the notes were written on (if it's crinkled, balled up, charred), or if the writing was too light and not easily visible for example.
Lack of a representative sample means that the message was too short, not enough letters were used, and there just isn't enough in the two samples to compare them.
There are variations in angularity, slope, speed, pressure, letter and word spacings, relative dimensions of letters, connections, pen movement, writing skill, and finger dexterity.
Other areas associated with writing also further the uniqueness of a given sample - margins, spacings, crowding, insertion, alignment are all personal habits.
If there is a suspect in custody and is asked for a sample, they're probably going to do their best to change their writing.
A better option would be to obtain a sample from their home or office that you know they've written while not under duress.
Positive findings can be made in most examinations, given that sufficient questioned material and known samples are available.
It is usually possible to say if a signature is a forgery, but unfortunately it is often not possible to say who forged it.
Combine that with spelling, punctuation, grammar, diction, etc., and you've got a completely one-of-a-kind document.
One key point for all comparisons is that they must be compared to a similar sample.