Yellow Ticks on Technology Cards

[JohnnyCyclops]

I notice yellow circles with a transparent tick mark appear on some but not all technology cards. What are they for please? It feels like a digital/online issue as I can’t see anything in the rules. It can’t denote upgrades as those are with the positioning and circle/square icons.

[poserLX]

This is a feature that exists on BGA to help players see at a glance if a tech card qualifies yet to be upgraded to square. Every tech card has prerequisites for upgrading to square, but you may not see the icon you mention until the game thinks it needs to bother checking for you. For example, if a tech card is still at X (hasn't been upgraded to circle yet), it's not as necessary to indicate whether or not it qualifies for square yet.

[JohnnyCyclops]

This is a feature that exists on BGA to help players see at a glance if a tech card qualifies yet to be upgraded to square. Every tech card has prerequisites for upgrading to square, but you may not see the icon you mention until the game thinks it needs to bother checking for you. For example, if a tech card is still at X (hasn't been upgraded to circle yet), it's not as necessary to indicate whether or not it qualifies for square yet.

Thank you. Makes total sense now you say it. Mid-game and I can see why some are ticked and others not.

[Isadavaba]

I agree with poserLX above, be aware though that a special tapestry card (Golden Age) that allows you to upgrade a card during your era without meeting the requirement will make the yellow circle appear, but it won't disappear after the end of the era (even if you can't meet the requirement).
I sadly don't have tables to show you where it happened but it can happen.