If you read through the marksmanship pages, you are probably wondering how you can manage all that in the field. Few snipers carry a computer with them (although this is becoming more frequent as devices become smaller, lighter and tougher)!
This is where the cheat book comes into play. The cheat book is a quick reference book you carry with you. In there you put all the data you need, calculated in the comfort or your home. I use a small 3x5 memo book and cover the pages with transparent plastic.
Since you are working in 2 man sniper teams (at least!) you must include the data for you and your fellow team member. This way there are two copies of all data and both team members can spot for the other.
This is what I have in my cheat book:
You should also have another book which lists the size of known objects in your area of operation. This is very helpful for range estimation.
Police snipers should measure traffic sings, cars, license plates, light posts, mail boxes, etc. They should also know the construction standards in use for doors, side walks, ... It is a good idea to measure some potential intervention sites like banks, government offices, hospitals, and schools.
Army snipers need a book with equipment, weapons and vehicles measurements. Measure both friendly and enemy equipment.
What is a 0 table? Every day look at the temperature and humidity levels. It you do not have a confirmed 0 for that combination, go to the range and confirm your 0. Fill the table with that data. As time goes on, you will have a complete record of 0 corrections for varying temperature and humidity levels. This is most useful when a real shot needs to be taken.
Special legal note for the cheat books (and other training records): Especially police snipers beware! Any cheat book, training record, rifle book could be used against you in court. Be careful what you write in there, consult a knowledgeable lawyer. I assume no responsibility for your cheat book or any other documentation you have!