Jon Peltier
I have tried your solution but it doesn't seem to work it throws up an error #N/A in both formulas.
I used the following formulas
=MATCH(H20,E15:E27) which is in H22
=(H20-INDEX(E15:E27,H22))/(INDEX(E15:E27,H22+1)-INDEX(E15:E27,H22))*(INDEX(F15:F27,H22+1)-INDEX(F15:F27,H22))+INDEX(F15:F27,H22) which is in H25
The value in H20 = 45.05
The table is below of which the 80 in the table is in E15 and the 2.62 is in F15
Could you please help to resolve.
[TABLE="width: 125"]
<tbody>[TR]
[TD="class: xl65, width: 64, bgcolor: transparent"]80
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]2.62
[/TD]
[/TR]
[TR]
[TD="class: xl65, width: 64, bgcolor: transparent"]75
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]2.26
[/TD]
[/TR]
[TR]
[TD="class: xl65, width: 64, bgcolor: transparent"]70
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]2.03
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]65
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]1.826
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]60
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]1.7
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]55
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]1.578
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]50
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]1.464
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]45
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]1.348
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]40
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]1.254
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]35
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]1.166
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]30
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]1.09
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]25
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]0.986
[/TD]
[/TR]
[TR]
[TD="class: xl64, bgcolor: transparent"]20
[/TD]
[TD="class: xl65, width: 103, bgcolor: transparent"]0.922
[/TD]
[/TR]
</tbody>[/TABLE]