Why are you so concerned with the display? The important thing is the temp of the water hitting the coffee. The display is showing you what it is reading inside the boiler minus the offset. As you are aware the difference is as much as 18 degrees. That difference can change as well by a number of different things. First of all since the water line that feeds the group boiler goes through the steam boiler there will be a slight difference if you are making coffee with the steam boiler on vs off. Things can also change in summer vs winter things like air conditioners or lack there of can change things slightly. You can also change things by changing PID settings make it either more or less aggressive. Don't try to fix something that is not broken. In many cases you WILL break something like trying to remove a sensor probe that there is nothing wrong with. The purpose of a dual boiler machine is to give you consistent temperature AT the coffee without the need of doing cooling flushes, i.e repeatability with little to no difficulty. Develop a routine, for example pull exactly two ounces with the portfilter in place then pull it out dry it put your coffee in there and when the temp is back up to it's peak pull your shot. If you do not like the taste try another setting. Usually speaking if the shot is very bright and you taste it on the front of your tong you are on the low end of the coffees best brew temp. If you taste the coffee in the back of your mouth you are close to the high end of the coffees desirable brew temperatures. Cross the low end and your coffee will taste sour cross the high ends and your coffee will be bitter. Find what you like and you can repeat it over and over. If you are insistent that you want to read temps in 1/10th of a degree then you need to spend two and half times as much money and buy a GS3.