# Error IsNumber function undefined

#### UHsoccer

##### Well-known Member
When using the following

If IsNumber(Range("B41")) = True Then

It returns a message "Sub or Function not defined

If it requires an "Install" of sorts, how can I insure that my customers have it also?

### Excel Facts

VLOOKUP to Left?
Use =VLOOKUP(A2,CHOOSE({1,2},\$Z\$1:\$Z\$99,\$Y\$1:\$Y\$99),2,False) to lookup Y values to left of Z values.

#### just_jon

##### Legend
The VBA function is IsNumeric -- can use Application.WorksheetFunction.IsNumber as well.

There ARE differences between the two, however. I'll try to find a good write up on that.

#### Nimrod

##### MrExcel MVP
Public Sub Demo()
If IsNumeric(Range("B41")) And Not IsEmpty(Range("B41")) Then
MsgBox ("is number")
Else
MsgBox "Not number"
End If
End Sub

NOTE: Anything that returns a boolean value (eg True/False) does not require you to ask if it equals. For example in the above procedure since IsEmpty and IsNumeric both return a boolean value I have not had to say
IsNumeric(Range("B41")) = False .... instead just use IsNumeric(Range("B41"))

#### just_jon

##### Legend
For a discussion of the diffs between the two, see this thread.

#### Juan Pablo González

##### MrExcel MVP
One important difference:

Code:
``````?IsNumeric("2"),Application.IsNumber("2")
True          False``````

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