Martin Guitar Company 0-45s stephen stills ユーザーガイド

Neck bow itself is often misunderstood and talked about as 
if it is the worst thing that can happen to a guitar. For some
playing styles, a slight forward bow can prevent buzzes. 
With the adjustable neck rod, the neck can be adjusted for 
relative straightness. This is not considered to be a consumer
adjustment and should be made by properly equipped 
Martin authorized distributors.

Sometimes sighting down the neck gives the illusion of neck
bow when it is actually within specifications. This is because
the top will rise and fall with changes in temperature and
humidity. This swelling raises the end of the fingerboard,
which is actually attached to the top rather than the neck. 
If this should become too high, it might need adjustment 
or repair.

The bellying of the top is normal and should be expected. 
The top is actually made with an arch. This will increase over
a period of time due to string stress and/or high humidity.
Heavy-gauge strings should not be used. If the bellying
becomes excessive, the saddle and bridge may need to be
lowered to improve the playability.

The guitar probably travels more than any other musical
instrument in the world, and it’ll only be a matter of time
before you take yours on its first trip. If you’re going to take
your guitar on the road with you, remember, it’s not just
another piece of baggage. You have to make an effort to 
protect it.