I have the LCD verison of this , mine takes a Parker brand refill , most office supply store sell these .
After removing the timepiece ,, at the end of the pen section there is a cap , this holds the cartridge in .
Unscrew it and the refill should drop out .
Your might be differnt than mine , Im not sure .
It should just pull apart between the clock and the pen section .
Got any pictures of it ?
Do you twist yours to raise and lower the pen tip?
or is it a CLICK type ?