"Pay particular attention to threads about the battery that powers the meter.
Mercury cells (1.3 volts)...they're no longer available.
Newer 1.5 volt replacements = wrong voltage in = wrong meter result out."

Meter isn't much good anyway. Best to use a handheld incident or spot meter.

Made my first professional pictures with one of them.
Used a bunch of them over the years.
Lens is best at f8 or 11.
You can get amazingly good results with the sports finder - zone focused @f8 with a flash.
The old guys I learned from always fired a flash on every frame - for fill on outdoor shots - and it definitely boosts the contrast.
The lens is sharp enough but its slow and prone to flare as compared to contemporary 35mm optics.
A lens hood, should you be lucky enough to find one, is mandatory.
The bayonet mount auxiliary wide angle and telephoto lenses (also rarely found) are passable as well if you use them within their limits.

That said, the old Yashicamat will teach you a lot about medium format photography for a very modest investment.