Try
Sheet1.chkTweak

(you can probably get away without the 'Call' too)

The Sheet1 above is the sheetname as shown in the Project Explorer
Pane of the vbe (the name not in brackets). You'll probably have to
change 'Private' to 'Public' too.

Instead of writing the bulk of your code  in the code module for the
sheet, it may be better to write it in a standard module and call  it
from the ChkTweak event handler, and from anywhere else for that matter.