You got the cheapest calibrator available on the market (around 12 euros or 15 USD) which does not even have a stated accuracy and which scale, I assume, barely has read-out precision of 1 or 2 kg. I would suspect that it is more likely the calibrator than the tensioner that is off.
This is what Wise has to say about calibration in the FAQ section on their web page:
“Can I calibrate the machine?”
After every pull the machine resets its zero point and checks its electronics. If you have a scientific gauge to measure tension we can tell you how to calibrate the 2086 from the front panel. A spring calibrator is usually not accurate enough. At any time the machine can be sent to Wise USA for a free re-calibration checkup. We only charge for return shipping. Or, you can verify the accuracy of the 2086 using the precision of the Tennishead™ 2090, our professional programmable calibrator.
To put things into perspective, electronic tensioners are quite accurate by design and require high accuracy gauges for calbration. Mechanical tensioners may be off by much more, and spring based gauges tend to be useful and accurate enough for them. I remember there was a used NEOS offered for sale (I assume, by one of the customers) through the local tennis shop. While I already had an electronic machine, I was curious to learn how NEOS works, and store employees were happy to share their knowledge. I brought my 2090 calibrator to the store and found that its tensioner was somewhere around 15, if not 18 Lbs off - I cannot remember the exact number, but I was astonished how much off it was. A spring calibrator would go long ways with that machine to bring it back to calibration.
When you had a crank on your machine, the calibrator which you have was the right tool, but with Wise you need an upgraded calibrator as well.
