It's easy to over-complicate and over-analyse this.
It's just a meter. It measures light energy and provides us with what will be a very accurate figure, which we then interpret and make use of.
The meter doesn't know how accurate the camera shutter is (actually modern shutters are pretty good, the older ones were often terrible)
It doesn't know how accurately the lens aperture will be set by the camera. There can be a fair bit of variation.
It doesn't know how much light the lens will actually transmit. Transmission can be affected by the lens coating and by the number of surfaces, i.e. a simple lens, all things being equal, will transmit more light - and sometimes a lot more - than a complex zoom lens.
And it doesn't know whether the manufacturer of a particular camera has exaggerated the ISO figure, and if so by how much. No names no pack drill, but that's one of the reasons I use Nikon cameras
So, as Kris said, we have to calibrate the meter to set our camera. Or, to be pedantic, we have to calibrate it to suit our camera/lens combination. Most of us don't of course, we just know that a certain camera/lens combination need say a half stop more than another, and adjust the settings without concious thought.
With
negative film, and especially negative mono film, there was any lattitude not to have to worry about it, within reason. In fact, those of us old enough used to guestimate our exposures because cameras didn't have built in meters (and those that did were pretty hopeless) and we couldn't afford hand held meters - and anyway they were only accurate in bright light.
Positive film though was very different. The lattitude on colour trannys was virtually non existent and to play safe, when in doubt we would always under expose a bit, because at least the info isn't destroyed by a mild degree of
underexposure and the opposite happened if we
overexposed.
That applies to digital too. Underexpose a bit and all the info will be retained. Overexpose and you lose detail in the highlights, the only real difference is that we can correct even fairly serious underexposure in digital. When digital was fairly new, a lot of people worried about underexposure because of the digital noise it used to create in the shadows, but modern cameras and modern software are so good that we don't need to worry too much.
So, after compensating for any idiosyncrasies of your particular camera/lens combination, interpret the correct exposure from the hand held meter reading and then interpret that data for the effect you want to achieve.
Then set it on your camera. If your meter says f/8 d5 and your camera doesn't allow you to set halfway between f/8 and f/11, set it to 2/3rds of the way instead (f/10) erring on the side of underexposure. That's plenty near enough.
I'm sure that a lot of photography beginners would be happy if lens apertures were logarithmic (1, 2, 4, 8 etc) but they're not. If you don't understand the maths behind f/numbers, just set your camera on aperture priority and fiddle with the setting dial, button or whatever and see what you get...
For example,
f/5.6 to f/8 is a whole stop. But on most cameras, it goes from f/5.6 to f/6.3 (1/3 smaller than f.5.6) then f/7.1 (2/3rds smaller than f/5.6) before going to f/8. Learn the 1/3rd increments for all aperture settings and then you'll be able to answer these questions instead of asking them
