How do I recognize characters on the 10-key?

I am attempting to trap special keys on the keypad for a high-speed
dataentry application. It MOSTLY works, however it does not work on every
computer. IOW, Keys.Divide, Keys.Multiply, and Keys.Subtract do not always
fire on some machines and I don't see an OEM equivilent for these.

I am using the following format:

private bool HandleKeys(Keys keyCode)
{
bool ret = false;
switch (keyCode)
{
case Keys.Enter: ret = EnterKeyPressed(); break;
case Keys.Add: ret = AddKeyPressed(); break;
case Keys.F1: ret = F1KeyPressed(); break;
case Keys.F2: ret = F2KeyPressed(); break;
case Keys.Divide: // used by ten-key data entry
case Keys.F3: ret = F3KeyPressed(); break;
case Keys.F4: ret = F4KeyPressed(); break;
case Keys.F5: ret = F5KeyPressed(); break;
case Keys.Multiply: // used by ten-key data entry
case Keys.F6: ret = F6KeyPressed(); break;
case Keys.F7: ret = F7KeyPressed(); break;
case Keys.F8: ret = F8KeyPressed(); break;
case Keys.Subtract: // used by ten-key data entry
case Keys.F9: ret = F9KeyPressed(); break;
case Keys.F10: ret = F10KeyPressed(); break;
case Keys.F11: ret = F11KeyPressed(); break;
case Keys.F12: ret = F12KeyPressed(); break;
default: ret = false; break;
}
return ret;