Calibrate soundlevels recorded from microphone with data measured from sound meter

I have to do  a long term meeting of soundlevels. I use a condenser
microphone  and a cheap soundmeter.

My plan is frpm one speaker 1 meter from the microphones  send sine
waves and place the sound meter beside the microphone. Record the
sound  then adjust the line in level so the in-signal is the same as
measuered on the soundmeter.

The results from the following measuremt will be 1 minute long  wav
files and a plot from the file.
I plan to record the files once each ten minutes.

So : How do I compare  data from recorded files and calculate the
correct decibel-levels.?

And why I not use a better sound-meter plugged in to the computer, it
is becasue they all have to bad range in frequenzy..

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