How to plot a “best straight fit” in Excel
1. Prepare a graph with all your data points. Use the average value for the T0.
Example (text in Icelandic):
32
Hitastig [°C]
31
30
29
28
27
26
25
0
50
100
150
200
250
300
350
Tím i [s]
2. Use only the data from the measured maximum T to the last value. You should get a
line with negative slope.
32
31,5
31
Hitastig [°C]
Click on any data point on your
graph. Click on the right mouse
button and select “Add
Trendline...”. A menu appears.
“Type” should be “Linear” and in
“Options”, select “Display
equation on chart”. Equation for
the best line fit appears on the
graph, y = ax + b. The maximum
T (the temperature that would
have been reached if no heat loss
to the surrounding) is then the
intercept to the y-axis.
30,5
30
29,5
y = -0,01x + 31,902
29
28,5
28
0
50
100
150
200
Tím i [s]
250
300
350