I just took your sample data, plugged it into a table and inserted a chart
into a form.

Using the wizard, I chose a Line Graph, with the orientation you described.
Yes, the Chart Wizard mangled it completely, but once it was done, I went
back to the properties of the graph, and changed its rowsource from what the
wizard generated to a simple SELECT [Time],[Temp] FROM [Readings] and the
resultant graph looked fine to me.

BTW, Time isn't a good choice for a field name: it's a reserved word, and
using reserved words can lead to problems. I'd recommend changing it to
something like ReadingTime.