Interpolation problems

kwinisy

New Member
Joined
Sep 12, 2014
Messages
2
hey guys. i am having problems with interpolation. our teacher taught the forecast method, but I tried applying it on my project it doesnt work. i mean the forecast method worked but the returned value isn't the right answer if you are to check in on a calculator.

AB
1PRESSURE0.12
2TEMPERATURE

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</tbody>
i named the columns P and T so this is my formula
on cell b2 i entered "=IFERROR(VLOOKUP($B$1,P,FALSE),FORECAST($B$1, T,P)"
the returned value is 204.4886
but if you will compute it on a calculator the answer is 39.65
HOW CAN I IMPROVE THE FORMULA?:confused:
P(psia)T (⁰F)
0.088632
0.09634
0.10436
0.112538
0.121640
0.131442
0.141944
0.153146
0.165148
0.17850
0.191652
0.206354
0.221856
0.238458
0.256160
0.274962
0.29564
0.316366
0.338968
0.362970
0.388472
0.415574
0.444276
0.474678
0.506880
0.540982
0.57784
0.615286
0.655588
0.698190
0.743192
0.790694
0.840796
0.893698
0.9462100
1.0079102
1.0697104
1.1347106
1.203108
1.275110
1.351112
1.43114
1.513116
1.601118
1.693120
1.789122
1.89124
1.996126
2.107128
2.223130
2.345132
2.472134
2.605136
2.744138
2.889140
3.041142
3.2144
3.365146
3.538148
3.718150
3.906152
4.102154
4.307156
4.52158
4.741160
4.972162
5.212164
5.462166
5.722168
5.993170
6.274172
6.566174
6.869176
7.184178
7.511180
7.85182
8.203184
8.568186
8.947188
9.34190
9.747192
10.168194
10.605196
11.058198
11.526200
12.011202
12.512204
13.031206
13.569208
14.123210
14.696212
15.592215
17.186220
18.912225
20.78230
22.79235
24.97240
27.31245
29.82250
32.53255
35.43260
38.53265
41.86270
45.41275
49.20280
53.24285
57.55290
62.13295
67.01300
72.18305
77.67310
83.48315
89.64320
96.16325
103.05330
110.32335
117.99340
126.08345
134.60350
143.57355
153.01360
162.93365
173.34370
184.27375
195.73380
207.74385
220.32390
233.49395
247.26400
261.65405
276.69410
292.40415
308.78420
325.87425
343.67430
362.23435
381.54440
401.64445
422.55450
444.28455
466.87460
490.32465
514.67470
539.94475
566.15480
593.32485
621.48490
650.65495
680.86500
712.12505
744.47510
777.93515
812.53520
848.28525
885.23530
923.39535
962.79540
1003.5545
1045.4550
1088.7555
1132.4560
1179.4565
1226.9570
1275.8575
1326.2580
1378.1585
1431.5590
1486.6595
1543.2600
1601.5605
1661.6610
1723.3615
1786.9620
1852.2625
1919.5630
1988.7635
2059.9640
2133.1645
2208.4650
2285.9655
2365.7660
2398.2662
2431.1664
2464.4666
2498.1668
2532.2670
2566.6672
2601.5674
2636.8676
2672.5678
2708.6680
2745.1682
2782.1684
2819.5686
2857.4688
2895.7690
2934.5692
2973.7694
3013.4696
3053.6698
3094.3700
3135.5702
3177.2704
3208.2705.47

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</tbody>

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Excel Facts

How can you automate Excel?
Press Alt+F11 from Windows Excel to open the Visual Basic for Applications (VBA) editor.
FORECAST interpolates a linear trendline, and the data is not linear at all. This interpolates a monotone ascending series:

C​
D​
E​
F​
G​
H​
1​
P(psia)​
T (⁰F)​
P​
T​
2​
0.089​
32​
0.12​
39.64823​
G2: =PERCENTILE($D$2:$D$205, PERCENTRANK($C$2:$C$205, F2, 6))
3​
0.096​
34​
4​
0.104​
36​
5​
0.113​
38​
6​
0.122​
40​
7​
0.131​
42​
8​
0.142​
44​
9​
0.153​
46​
 
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