Chow_13answered grow question 2 years ago I have 2 meters and when they are not in sync then I will use a cleaner and change the batteries.
Another option is to check using an EC calbration solution
https://www.amazon.com/s?k=ec+solution&crid=180B5ZQ6GK89R&sprefix=ec+solution%2Caps%2C98&ref=nb_sb_noss_1
Lastly you can also look at the manufacture feed chart which usually has EC values listed. These "Should" line up when you use RO water.
I use the blue lab prob cleaning solution with a toothbrush on my cheap amazon pens.
https://www.amazon.com/CAREKITCON-Conductivity-Solution-Controller-Hydroponic/dp/B00GG9C0XO/ref=sr_1_3?crid=2DO3VLWJE8H4B&keywords=ec+pen+cleaner&qid=1669736487&sprefix=ec+pen+cleaner%2Caps%2C90&sr=8-3