With the flash service that includes the pack you have a custom firmware that allows you to choose, with the keys g+enter+on+4, between the firmware of 15, an improved version 15.2 or that of 16c (as seen in the photo)
Another option would be to buy this fantastic modern clone:
As much as I love the SwissMicros line of calculators, the price is a little too much on the exorbitant side. If I was going to go with something not actually HP, the PX-16C is much more my speed and looks like a fun afternoon project, too.
Does the overlay come with it? The 16C has been on my list for a long time, but I didn't know that the 15C collectors edition had that capability!
I bought it in: https://www.thecalculatorstore.com/epages/eb9376.mobile/en_US/?ObjectPath=/Shops/eb9376/Products/HP15c_Enhanced
With the flash service that includes the pack you have a custom firmware that allows you to choose, with the keys g+enter+on+4, between the firmware of 15, an improved version 15.2 or that of 16c (as seen in the photo)
Another option would be to buy this fantastic modern clone:
https://www.swissmicros.com/product/dm16l
As much as I love the SwissMicros line of calculators, the price is a little too much on the exorbitant side. If I was going to go with something not actually HP, the PX-16C is much more my speed and looks like a fun afternoon project, too.