I have a spreadsheet in which a new row of data is put in for a date.  General layout is 1st column = Date and each column in that row is the value associated for that date.  

I chart this data using a lint chart, and always want the last 25 days o show on the chart.  For this particular chart, the x-axis is the date and is A5:A29, and a line on the chart may be N5:N29.  

For each new date, a row is inserted at the top of the table, and the new data are entered for that date/row.  When I view the chart, the data range for the chart changes to A6:A30; N6;N29. 

How do I set this up so that the chart always shows the last 25 days, without manually changing the chart range each time?