HELP with Temperature probe - seems to read different value

[Franklin]

I´ve got my GHL temparature probe installed since 3 weeks now and the reading was more or less close with an manual temperature probe (an wine temp stick). The reading was around 25,5C, the last few days the GHL probe read over 27,1 / 27,3. What ever i did to drop the aquarium temperature the values are still very high
In comparison to a manual temp reading, the probe/device is reading an approx 1 degree C diff.
Questions: what do i have to trust, the GHL probe or manual temperature reading. Now what to do?

please find enclosed screen shot