Here’s a practical cut for anyone doing caulking with silicon (@geek2nurse?). Unlike tile caulk it’s not supposed to be shoved into the joint - it’s supposed to sit with a straight edge, like a triangle attaching on the two sides of the front -and not filled in behind. To that end there are, not inexpensive, objects one can buy to give you that straight front edge…but I have a laser and scrap acrylic
Engraved numbers are in millimeters - but even when the job is well done you may find yourself switching between edges.
Sadly for me the folks who installed my surround did a terrible job and the overhang made it almost impossible for me to use these - but in a few places they were brilliant.
Hopefully they can help someone else out!