Excel 2007 : Show Last 25 values in Chart

I've got a chart with some dollar values that are all listed in Column I and get updated each time I add an entry to the sheet.

What I'd like to do is have my chart dynamically adjust to show only the last 25 values I've entered.

I've attempted this with the offset formula but I'm quite a bit confused by it and didn't have any luck.

Column I
 $145.00 
 $140.00 
 $144.55 
 $153.64 
 $143.64 
 $148.19  < Show from this value down to the bottom of the list.
 $138.19  < When new value is added, show from this value to the bottom of the list.
 $128.19 
 $137.71 
 $127.71 
 $145.00 
 $140.00 
 $144.55 
 $153.64 
 $143.64 
 $148.19 
 $138.19 
 $128.19 
 $137.71 
 $127.71 
 $145.00 
 $140.00 
 $144.55 
 $153.64 
 $143.64 
 $148.19 
 $138.19 
 $128.19 
 $137.71 
 $127.71

Thanks

In terms of OFFSET

OFFSET($I$1,MAX(0,COUNT($I:$I)-25),0,MIN(25,COUNT($I:$I)),1)

A non-volatile equivalent would be:

INDEX($I:$I,MAX(1,COUNT($I:$I)-25+1)):INDEX($I:$I,MATCH(9.99E+307,$I:$I))

per the OFFSET it is assumed the numbers are always contiguous

I'm no Charting whizz I'm afraid but below should work:

Name: _ChtData
RefersTo: =OFFSET($I$2,MAX(0,COUNT($I:$I)-25),0,MIN(25,COUNT($I:$I)),1)

Name: _ChtDataFinal
RefersTo: =Evaluate("_ChtData")

Right click on your Chart, Select Data then select "Balance" and click Edit and set Series Values as:

=(Sheet1!$O$3,'Help (3).xlsx'!_ChtDataFinal)

I can't find any other way (other than Evaluate) to have the Dynamic Range persist but as mentioned I am no charting expert - plenty here are and are likely to have better alternatives.