Single letters are filed before double letters:
Q 
QC 
QL 
R 
RA 
The second part of a call number is made up of a number that may have one or more digits. This line is read numerically. A call number with a smaller number is shelved before one that has a larger number. Some of these numbers may be divided by a point: these are also read numerically (smaller numbers are shelved before larger numbers).
QA

QA

QA

QA

QA

QA

QA

QA

QA

The third part is the trickiest part of the call number. This part of the call number is called the "cutter". The numbers in this part are treated like decimals.
Follow these general rules when dealing with cutter numbers:
QL

QL

QL

QL

QL

QL

QL

QL

QL

QL

QL

Sometimes there are TWO cutter numbers in a call number. The first cutter, in these cases, is related to the subject of the work. The second cutter is related to the author. The shelving order of the second cutter follows the same four rules described above.
QE

QE

QE

QE

QE

QE

QE

QL

QL

Sometimes, the top of the call number has the item's location: "Ref" for Reference room, etc. The final lines of the call numbers may include copy numbers, issue numbers, volume indicators and other annotations such as supplement or index specifiers. For example, the call numbers below are shelved in Reference:
Ref.

Ref.

Ref.

Ref.

Ref.

How to read the decimal in call number:
K383.12 comes before K383.5 because .12 is a smaller decimal number than .50. Similarly, KF250.39977 comes before KF250.4 because .39977 is a smaller decimal tnumber than .40000.
Always keep in mind when shelving books and shelfreading: that nothing comes before something
If a book contains no volume number, that book comes before a book within a set that does contain a volume number. If a book contains no date in the call number, that book comes before the same book that does have a date in the call number.