> the four pin units are probablly oscilator modules,......they are
> expensive and take up a lot of space

And use a lot of power and can't be shut off (well, they can if
you switch the supply) like the PIC's oscillator does when it
sleeps. Unless you really need one - driving more than one PIC,
need synchronised logic, that sort of thing - don't bother

I usually solder the crystal's case to 0V, either to a pad or with a
short link of wire. A couple of projects had problems if that wasn't
done, so I do it routinely now

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