The use of a good, stable multifunction meter is a good start.
Here in the States, we have a pretty stable 120 VAC, and in
some places, it reads 125 volts, with a frequency of 60 cycles
per second. At least where we live, our Electricity Supplier
gives us a very stable 60 cycles. This is one good reason why
our Digital Alarm Clocks keep very good time, because the
Microprocessor within is using the 60 cycles off of the line as
it's time base. Most outlet(s) in the kitchen will be supplied by
(a) 15 amp breaker(s) located at the load center. This should
be enough power to operate any kitchen appliance meant for
residential use. A real test would be the use of an Amp Clamp
around the hot wire connecting to the breaker feeding the
outlet that has a microwave oven plugged into it. Let me talk
about electrical safety, before we remove the cover off of the
Load Center. First, make sure that the floor is clean and dry.
Second, always wear clean and dry socks and shoes. Third,
wear eye protection. Fourth, never rest your free hand inside
the bottom of the load center, or on any point of ground. Fifth,
wear clean, dry gloves (at least clean on the inside) on both
hands. Sixth, make sure that you have plenty of light so you
can see what you are working on clearly. Now, after
understanding all of this, and you have the Load Center well
lit and are properly dressed; you can now safely remove the
cover of the Load Center. Locate the breaker that operates /
protects the kitchen outlet that the Microwave Oven is plugged
into. Place the amp clamp around the wire coming from this
breaker. Place a bowl of water in the oven and set the timer
for 1 min. +30 seconds. Start the oven and go back to the
Load Center. The Amp Clamp should read about 7 to 8 amps,
depending on the oven being used. Also, note the voltage, once
the Microwave's Magnetron "keys up". The voltage will slightly
dip down 2 or 3 volts, as the current rises. A Space Heater is
a good test as well, and requires no bowl of water. Whenever
working on any electrical and / or electronic equipment, follow
the above directions, and you will remain safe. Never work on
live equipment. Always Lock Out And Tag Out (keep the kids
away and out of the room). If there is an issue with your Load
Center, contact an Experienced, Certified Electrician to inspect
your equipment. Feel free to e-me. Happy Holidays!