We have received several questions about the Overlay option in the HP15CE - so many that we have changed the name to "Cover".
It is an HP16c overlay to be put on top of the keyboard. It allows the machine to behave as an HP16c if you have the means to transfer there the firmware of an HP16c. It is possible on the newest versions of the HP15c or the HP12c too (NOT Platinum). More details to come in following weeks!
There will be another option for HP15c cover too.