[gpm] History graphs - issues and possible improvements

[Phil Sherman <psherman ameritech net>]

A recent upgrade to FC5 and a failing battery have encouraged me to
attempt to use the history graphs to determine what is happening to the
battery. The graphs are difficult to interpret because the X axis
labeling is confusing. All three graphs appear to use the same scheme to
show a time value. 

My interpretation of the X axis is that the the graph shows the most
recent 10 minutes of power information. The x axis zero point appears to
be the last power on time. Graph data propagates from left to right with
the most recent information located at the right end of the data. Once
the data reaches the right side of the graph, additional data pushes all
plotted data to the left by half the graph width then new data continues
to grow the graph to the right. I was unable to discover any information
about this in the documentation. The location of the zero point also
requires continuing updates to the x axis labels.

These are very difficult graphs to interpret and don't provide enough
data to fully evaluate a battery. The graph would be easier to interpret
if the new data were inserted at one side of the graph; forcing all
prior data to move to the opposite side. Unfortunately, this requires
significantly more overhead to maintain than the current scheme. It
should also require significant changes to the existing code.

There is, however a different display scheme that would improve the
readability and should use almost all of the existing code. This format
would do the following:
1. Divide the graph horizontally into two sections. The left hand side
would represent history, the right hand side would represent the future.
The dividing point would be labeled with the time of the past/present
division.
2. Label the x axis with positive or negative displacements from the
division time or use that information to compute the actual time for
labels. Displacements don't need to be updated while time values are
easier to interpret. Labeling can be simplified by using integer values
and an initial displacement for the first data point to be plotted.
(ie.If the division time were 8:01 and recording started at 8:01:30 then
the first data point would be displaced 0.5 minute on the future side.)
3. An interesting option of this is to display history in hours and
future time in minutes. This would show the last five hours of history
with the most recent zero to five minutes shown in fine detail.

Keeping four to 10 hours of history would provide a full log of a charge
or discharge cycle. Five hours history with five minutes future is an
interesting option because the current code records 12
intervals/division which would nicely place an ending five minute future
period into a single display point of a five hour history.

If anyone has other ideas or comments, I'd appreciate your posting
replies.

Phil Sherman