Linear Interpolation with a lookup table

So, if I understand what you are saying, you want sensor ID=0 to only interpolate over your known entities table with a corresponding ID=0 and ID=1 should only interpolate over ID=1 known entities, correct? Let me know if that is correct, shouldn't be difficult at all to modify the formula. So, using my original formula, you could probably do something like below (which assumes that you have unrelated tables that both have an ID column 

Pressure (MPa)  = 
VAR x3 = MAX(Interpolation[Temp (C)]) //This is the known value for which you wish to interpolate another value

VAR __id = MAX(Interpolation[ID] // current ID

VAR match = CALCULATE(MAX(H2OTempSat[Pressure (MPa)]),FILTER(H2OTempSat,[Temp (C)]=x3 && [ID]=__id)) //checks if it is a known value

VAR x1 = CALCULATE(MAX(H2OTempSat[Temp (C)]),FILTER(H2OTempSat,[Temp (C)]<=x3 && [ID]=__id)) //low X value

VAR x2 = CALCULATE(MIN(H2OTempSat[Temp (C)]),FILTER(H2OTempSat,[Temp (C)]>=x3 && [ID]=__id)) //high X value

VAR y1 = CALCULATE(MAX(H2OTempSat[Pressure (MPa)]),FILTER(H2OTempSat,[Temp (C)]<=x3 && [ID]=__id)) //low Y value

VAR y2 = CALCULATE(MIN(H2OTempSat[Pressure (MPa)]),FILTER(H2OTempSat,[Temp (C)]>=x3 && [ID]=__id)) //low X value

RETURN IF(NOT(ISBLANK(match)),match,y1 + (x3 - x1) * (y2 - y1)/(x2 - x1)) //if a match, return match otherwise interpolate