Interpolating logarithmic vacuum sensor table

Projects General Guidance
9

Sources of error could include:

  1. The supply not being exactly 5V. Usb power is often 4.7-4.8V in practice. Powering the Arduino through its barrel jack with 7.5-12V may give something closer to 5V.

  2. The resistors in your voltage divider. If they have gold bands, they should be within 1% tolerance, but you could measure them to check.

If that does not get you close enough, there are other ways such as using the Arduino's internal voltage reference, or an external voltage reference (but never connect anything to AREF that is higher than Vcc).