I have to design a flex PCB with a 90 Ohm differential pair. (Edge coupled microstrip)

There are different calculators on the web to ease my life. My problem is: I don't know, which one gives the most reliable result?

When I enter the same properties, I got completely different values from different calculators.

Just as an example:

Board thickness (h) = 50 micron

Copper thickness (t) = 18 micron

Track width (w) = 137 micron

Distance between tracks (s) = 254 micron

Dielectric constant = 3.4

(Sorry guys, I live and I have grown up in a metric world )

With these values, Saturn PCB's off-line calculator gives 57 Ohm differential impedance.

Altium's on-line results 88.6 Ohm ( https://resources.altium.com/p/differential-microstrip-impedance-calculator )

PCBway's on-line gives 90.8 Ohm ( https://www.pcbway.com/pcb_prototype/impedance_calculator.html )

By Digi-Key I got an error message and it calculates 67.3 Ohm ( https://www.digikey.com/en/resource...ors/conversion-calculator-pcb-trace-impedance )

Multi-Circuit also has a calculator that gives 67 Ohm ( https://www.multi-circuit-boards.eu/en/pcb-design-aid/impedance-calculation.html )

Eeweb's calculator results 91.8 Ohms. ( https://www.eeweb.com/tools/edge-coupled-microstrip-impedance/ )

So, the election ended with 3:3 But I'm afraid, there's only one proper calculation.

None of the above calculators are able to give data on the standard 25 micron thick material for 90 Ohms.

Which one shall I trust? Do You have experience with these calculators? Unfortunately, I have no field solver and I don't feel motivation and knowledge to manually solve Maxwell's equations