Excel 2000

At various times during each day I have to measure my blood pressure. Each
time I take 4 readings (simplified version).

A: DATE B: TIME C: BP
A1: 01/01/2007 B1: 09:00 C1: 75
A2: 01/01/2007 B2: 09:01 C2: 77
A3: 01/01/2007 B3: 09:02 C3: 74
A4: 01/01/2007 B4: 09:03 C4: 77

I can generate a scatter chart with Days on the x axis, BP on the y axis and
the C data as vertical columns of short horizontal lines ( - ) for each day.

This method produces a good graphical representation of the range of the
day's readings, but multiple readings with the same value are only displayed
as a single point on the chart.

i.e. 1 off 74, 1 off 75 and 1 off 77

I still need to create a chart that will display every reading so I tried
using a helper column D with the values A+B i.e.

D1: 39083.375
D2: 39083.37569
D3: 39083.37639
D4: 39083.37708

I then used these values for the x axis and series range but this only
worked over a minute spread of D values before, once again, failing to
display multiple values correctly.

Quite probably a "senior moment", but any help would be greatly appreciated.

--
Fred