Single or Double?

[Guest]

Hi again,

Is there any rule for defining a number field to single or double? When I
want to define a field to accept money (up to now) I define it as number
single (I dont like the currency). Will this be a problem when adding the
values of this field (or get the avg)? What rules are applied for this
datatypes//fieldsizes?

Thanks in advance,

George

 

[Allen Browne]

Use a Double as the default, since it gives better accuracy. Use a Single
only when performance or disk space is critical, *and* accuracy is less
important. Typically, a Single gives you the first 7 or 8 significant
figures accurately, whereas the Double gives you around 15 significant
digits.

Why don't you like Currency? As a fixed-point data type, it avoids the
problems inherent in floating-point numbers. There are some things it's not
suitable for (e.g. if you need more than 4 decimal places or monstrously
large numbers that rely on being powers of 10.) But I regularly use Currency
for non-money fields (such as measurements in metres, accurate to 1/10th of
a millimetre) just because it avoids the floating-point issues.

 

[Guest]

Thanks a lot Allen for your prompt reply,

Just one more thing pls? What do you mean by saying "floating-point
issues". Sorry but my mother language is Greek.

Ο χÏήστης "Allen Browne" έγγÏαψε:

 

[Allen Browne]

The problems crop up when you compare 2 floating point numbers which look
equal but are not, when you add floating point numbers (e.g. in a loop), and
son on.

For details, see:
http://en.wikipedia.org/wiki/Floating_Point#Accuracy_problems

This problem occurs in all computer languages that use floating point
numbers, i.e. it is not specific to Access.