I think there is adjustment to bias the reading to what you like but it would effect flash reading as well.
I've read online that in use IF you read the Kodak instructions, you don't hold the card straight up but at an angle and when held at that angle it's actually 12.5%.
I believe this was from a writer of columns for one mag or another.
The meter can be calibrated to take into account filters e.g. +1.6 (varies for each filter). Baseline calibration is with ISO 1 and ISO 2 buttons pressed simultaneously.
The meter does not require any additional calibration on the premise of making sure the exposure is correct — that is your responsibility, gained through active experience using the meter.
I would ignore most online commentary regarding the Sekonic baseline mid-tone calibration: it is not particularly well-informed.
If you just got the meter, why do you suspect that it's off???
I had a 358 for several years, then replaced it with a 558 to get the spot capability.
I found both of them to be right on. Sekonic meters are accurately calibrated at the factory.
Proper exposure has a lot to do with your shooting and processing habits.
If the meter doesn't produce what you want after a lot of experimentation, then adjust it.
I use one, both in the studio and outside.
Never had any problems.
Remember that what your camera meters and what your meter is reading, can differ greatly, depending on what metering mode you have set your camera to, the meter doesn't have spot readings either, not matrix, not center weighted etc.
I don't know....I just trust it, but I make sure to meter correctly and several times to avoid any misreadings/errors on my part when I am outside.
Your meter has a built-in gray reference (the white dome), and your meter is calibrated to its own dome. As long as the meter is not out of whack, you should be able to use it with factory settings.
I enjoy discussing the different factors, but the bottom line of what I have learned is that the important factors are there for a reason and they are built into the calibration standards.
My simplest advice: Set the EI in your meter at the rated or actual speed of your film, and then change the EI if you find out you have to.
If you change the way you meter, like if you decide to start doing BTZS (Beyond the Zone System) metering techniques, then you might have to change your EI again.
Traditional Zone System spot metering with traditional N development often results in EI approximately half the rated speed. That's what I do and is why my EI is 2/3 stop "lower" than the actual speed of the film.
You'll be pleased to know that the incident light reading does NOT agree with a spotmeter reading off 18%. It agrees more closely with a spotmetering off the 12.7% patch!
I have 2 of the 358s and they are highly reliable.
No other piece of equipment I own adds more to any shot.
I can hardly imagine it providing you a problem.