time-scale axis problem

[Guest]

I have sets of data that have a date with a corresponding numerical value in
number format with one decimal. When I try to plot them on a line chart with
a time-scale axis, Excel defaults to putting my points between 1/1/1900 and
1/20/1900. If I change the dates, then all my points end up nearly
vertically on the y-axis and do not correspond to the dates on the x-axis,
even though the point will indicate the correct date if you point to it with
the mouse. My final goal is to evaluate the rate of change in the values,
which I hope to do by looking at the average slope of the line. Thanks for
your help.

 

[Guest]

An addendum to my question below: Additionally, if I use "Automatic" or
"Category" for the X-axis, then all the dates are plotted at equal distances
from each other rather than being scaled according to the time between them.
Again, the end result is that I need to evaluate the rate of change of these
values over time, so any way that I can do that either by chart or otherwise
will help me. thanks, Ronan

 

[Kelly O'Day]

Ronan:

Use an XY chart instead of a line chart.

 

[Guest]

When I use the XY chart I have the same problems with the dates not
corresponding to the x-axis. The charts are coming up with the x-axis being
the first several days of year 1900, and the dates of my data points don't
correspond. Also, I would like to know if there is any other way to look at
rate of change other than a graph with a slope of a line. Thanks, Ronan

 

[Kelly O'Day]

Ronan:

1. Excel does not recognize your X data as valid dates. Are you using
standard convention: 03/012007?

2. Rate of change: you can calculate the rate of change as ratio or you can
calculate compound rate of change r.

Basic compound interest formula: Value@ t2 = Value @t 1*(1+r)^n
where r is rate of change per unit time
n is number of time units.

If you have annual data, t1 would be 2005, t2 would be 2006.

Solving for r:

r= {[Value@t2/Value@t1]^(1/n)}-1



,..Kelly

 

[David Biddulph]

I think Ronan meant 03/01/2007. with the second slant, but this might be
01/03/2007, depending on your Windows regional settings and on your Excel
cell format.
--
David Biddulph

Ronan:

1. Excel does not recognize your X data as valid dates. Are you using
standard convention: 03/012007?

....