Spreadsheet: 132736d1323894719-real-time-curve-interpolation-excel-2007-example-2
Sheet: Sheet1

Actual data points |  |  |  | Interpolated
x | F(x) |  |  | x | F(x)
-0.6209 | 0.3562 |  |  | -0.8200000000000001
-0.5811 | 0.3479 |  |  | -0.8
-0.5415 | 0.33765 |  |  | -0.78
-0.5021 | 0.32593 |  |  | -0.76
-0.463 | 0.32007 |  |  | -0.74
-0.4242 | 0.30933 |  |  | -0.72
-0.3856 | 0.29858 |  |  | -0.7
-0.3473 | 0.29028 |  |  | -0.6799999999999999 |  |  |  |  |  |  | Below are just examples of how to solve for different order polynomials.  "INDEX", "kWh", and "AvgTemp" are just named ranges in one of my workbooks. You can change them to your ranges.
-0.3092 | 0.28247 |  |  | -0.6599999999999999
-0.2713 | 0.27368 |  |  | -0.6399999999999999
-0.2337 | 0.26636 |  |  | -0.6199999999999999
-0.1963 | 0.25903 |  |  | -0.5999999999999999 |  |  |  |  |  | 4th Order Polynomial Trendline |  |  | =(INDEX(LINEST(kWh,AvgTemp^{1,2,3,4}),1)*$A$45^4)+(INDEX(LINEST(kWh,[NAME]^3)+(INDEX(LINEST(kWh,AvgTemp^{1,2,3,4}),1,3)*$A$45^2)+(INDEX(LINEST(kWh,AvgTemp^{1,2,3,4}),1,4)*$A$45)+(INDEX(LINEST(kWh,AvgTemp^{1,2,3,4}),1,5))
-0.1592 | 0.25317 |  |  | -0.5799999999999998 |  |  |  |  |  | 3rd Order Polynomial Trendline |  |  | =(INDEX(LINEST(kWh,AvgTemp^{1,2,3}),1)*$A$45^3)+(INDEX(LINEST(kWh,AvgTemp^{1,2,3}),1,2)*$A$45^2)+(INDEX(LINEST(kWh,AvgTemp^{1,2,3}),1,3)*$A$45)+(INDEX(LINEST(kWh,AvgTemp^{1,2,3}),1,4))
-0.1222 | 0.24731 |  |  | -0.5599999999999998 |  |  |  |  |  | 2rd Order Polynomial Trendline |  |  | =(INDEX(LINEST(kWh,[NAME]^2)+(INDEX(LINEST(kWh,AvgTemp^{1,2}),1,2)*$A$45)+(INDEX(LINEST(kWh,[NAME]))
-0.0855 | 0.24341 |  |  | -0.5399999999999998
-0.0491 | 0.2395 |  |  | -0.5199999999999998
-0.0128 | 0.23608 |  |  | -0.4999999999999998
0.0232 | 0.23608 |  |  | -0.4799999999999998
0.059 | 0.23462 |  |  | -0.4599999999999997
0.0946 | 0.23364 |  |  | -0.4399999999999997
0.13 | 0.23364 |  |  | -0.4199999999999997
0.1652 | 0.23364 |  |  | -0.3999999999999997
0.2002 | 0.23462 |  |  | -0.3799999999999997
0.235 | 0.23706 |  |  | -0.3599999999999997
0.2696 | 0.23901 |  |  | -0.3399999999999996
0.304 | 0.2439 |  |  | -0.3199999999999996
0.3382 | 0.24829 |  |  | -0.2999999999999996
0.3722 | 0.25122 |  |  | -0.2799999999999996
0.406 | 0.25806 |  |  | -0.2599999999999996
0.4396 | 0.26343 |  |  | -0.2399999999999996
0.473 | 0.2771 |  |  | -0.2199999999999996
0.5062 | 0.28198 |  |  | -0.1999999999999996
0.5393 | 0.2937 |  |  | -0.1799999999999996
0.5722 | 0.30835 |  |  | -0.1599999999999996
0.6049 | 0.31958 |  |  | -0.1399999999999996
0.6374 | 0.32983 |  |  | -0.1199999999999996
0.6697 | 0.3396 |  |  | -0.09999999999999962
0.7019 | 0.34888 |  |  | -0.07999999999999961
0.7339 | 0.35718 |  |  | -0.05999999999999961
0.7657 | 0.3645 |  |  | -0.03999999999999961
0.7974 | 0.37085 |  |  | -0.0199999999999996
 |  |  |  | 0.02
 |  |  |  | 0.04
 |  |  |  | 0.06
 |  |  |  | 0.08
 |  |  |  | 0.1
 |  |  |  | 0.12
 |  |  |  | 0.14
 |  |  |  | 0.16
 |  |  |  | 0.18
 |  |  |  | 0.2
 |  |  |  | 0.22
 |  |  |  | 0.24
 |  |  |  | 0.26
 |  |  |  | 0.28
 |  |  |  | 0.3
 |  |  |  | 0.32
 |  |  |  | 0.34
 |  |  |  | 0.36
 |  |  |  | 0.3800000000000001
 |  |  |  | 0.4000000000000001
 |  |  |  | 0.4200000000000001
 |  |  |  | 0.4400000000000001
 |  |  |  | 0.4600000000000001
 |  |  |  | 0.4800000000000001
 |  |  |  | 0.5000000000000001
 |  |  |  | 0.5200000000000001
 |  |  |  | 0.5400000000000001
 |  |  |  | 0.5600000000000002
 |  |  |  | 0.5800000000000002
 |  |  |  | 0.6000000000000002
 |  |  |  | 0.6200000000000002
 |  |  |  | 0.6400000000000002
 |  |  |  | 0.6600000000000003
 |  |  |  | 0.6800000000000003
 |  |  |  | 0.7000000000000003
 |  |  |  | 0.7200000000000003
 |  |  |  | 0.7400000000000003
 |  |  |  | 0.7600000000000003
 |  |  |  | 0.7800000000000004
 |  |  |  | 0.8000000000000004
 |  |  |  | 0.8200000000000004