In one of these exercises, I sit quietly in a quiet place, close my eyes, put my right hand on my
right knee, my left hand on my left knee, and concentrate just on my two index fingers. Basic
dharma theory tells me that it is not possible to perceive both fingers simultaneously; so, with
this knowledge, I try to see in each instant which one of the two fingers’ physical sensations
are being perceived at any given moment. Once the mind has sped up a bit and become more
stable, I try to perceive the arising and passing of each of these sensations. I may do this for half
an hour or an hour, just staying with the sensations in my two fingers and perceiving when each
sensation is and is not there

Benjamin Schmidt My background in meditation is pretty limited .

Recently I chatted with someone from a Soto Zen background who described his Zazen practice to me. I understood his practice as sitting in the right posture with open eyes and trying to experience all sensations at once.

This seemed somewhat contradictory with the following excerpt from MCTB2: 

In one of these exercises, I sit quietly in a quiet place, close my eyes, put my right hand on my right knee, my left hand on my left knee, and concentrate just on my two index fingers. Basic dharma theory tells me that it is not possible to perceive both fingers simultaneously; so, with this knowledge, I try to see in each instant which one of the two fingers’ physical sensations are being perceived at any given moment. Once the mind has sped up a bit and become more stable, I try to perceive the arising and passing of each of these sensations. I may do this for half an hour or an hour, just staying with the sensations in my two fingers and perceiving when each sensation is and is not there

I would be interested in an explanation of what the idea behind the Zen practice is, maybe where something got lost or I missunderstood something in either practice.  Maybe the idea is just all the experiences which are there which would then just be the experience in the one fingertip, but I understood the person as experiencing different things from the same sense and different senses at once.

Bonus question: Using all these metaphysical/ontological assumptions about time and body existing and being responsible for our experience ... It seems there would have to be some limit to this where you can't infinitely split the experience into smaller parts which just happen quickly in order (e.g. one 1000000 experiences per second representing just the sensations on one fingertip). Is there a volume of body which can usually be assigned to one timewise inseparable experience? Is it maybe different depending on the number of nervendings in the area or something else.

Am I completely misunderstanding things ?

Everything all at once or everything separately

If you can perceive one sensation per second, try for two. If you can perceive two unique sensations per second, try to perceive four. Keep increasing your perceptual threshold in this way until the illusion of continuity shatters. In short, when doing insight practices, constantly work to perceive sensations arise and pass as quickly and accurately as you possibly can. With the spirit of a race car driver who is constantly aware of how fast the car can go and still stay on the track, stay on the cutting edge of your ability to see the impermanence of sensations quickly and accurately.

One of the other hallmarks of Equanimity is that the way reality presents is not made up of lots of little sensations occurring in some stable space, not broken up into lots of little, individual sense doors, but instead complete phenomena begin to be perceived as consolidated in a more integrated way, meaning that they are formed together, with space, awareness, and all the different types of sense qualities happening all together to make up the objects in the sensate world, and even all of those objects in the world arise in these integrated wholes, consolidated swaths of moving space that contain all those things within them. It is as though flowing space has textures, colors, sounds, tastes, smells all integrated into it, as part of it, and gradually attention and anything that really seems to be “us” finally gets integrated in the same way also, though we might not notice this at all. The thing about this integrated way of perceiving reality is that, at this stage, it just seems so normal that most people won’t have any idea that this is what is happening unless they are curious about the basics of the way attention and sensate information present themselves, or have been given a heads-up that this is what occurs at this stage. It sounds dramatic, but it is very undramatic. Many will get through this stage and have no idea that something was different, and that’s okay.

These put-together sense impressions, these formed things, are formally (pun intended) called “formations”, and they are the phenomena regarding which we come to Equanimity in this phase. The full formal name of this stage is Knowledge of Equanimity Concerning Formations. I put off writing about formations for a long time, since although the experience of them is very straightforward and natural, they are for some a conceptually difficult topic. Furthermore, the classical definition of “formation” is perhaps not so clear-cut, so I was concerned about imposing on the term my own functional and experiential definitions. Lastly, it seems that plenty of people will just get confused by this set of descriptions, and even plenty of talented meditators won’t be able to notice that these integrated formations are what is going on, and they clearly don’t have to for progress. However, as the topic comes up repeatedly, here we go …

Formations contain all the six sense doors, including thought, in a way that does not split them up sequentially in time or positionally in space. If you could take a 3D moving photograph that also captured smell, taste, touch, sound, and thought, all woven into each other seamlessly and containing a sense of flux, this would approximate the experience of one formation. From a fourth vipassana jhana perspective and from a very high dharma point of view, formations are always what occur, and when they are not clearly perceived, then we experience reality the way we ordinarily do. They contain not only a complete set of aspects of all six sense doors within them, but also include the perception of space (volume) and even of time, movement, and the sensate qualities that make up “duration”. This distinction between ordinary perception of formation and perceiving formations in the way that people do in Equanimity is a very subtle one, and so descriptions like those here can cause confusion if misinterpreted to imply some dramatic perceptual shift, as evidenced by the endless questions I received about this section after writing MCTB1.

As this experience matures another important shift occurs, and it is a very subtle one: it no longer seems as if the objects alone are vibrating, but rather that the entire field of awareness itself is vibrating. When this occurs the meditator begins to take the whole field of awareness itself as the object. All the things that are normally taken as objects still pop in and out of awareness, but now they are only part of what now constitutes the object, which is the vibratory nature of the whole field of awareness itself.

​​​​​​​At this point you may be asking yourself what is meant by “field of awareness.” Admittedly, it is a pretty geeky term, but it is a very useful one to know at this stage of development. A useful analogy is a movie projected onto a screen. You can pay attention to anything in the movie, the characters, the scenes, the dialogue, etc., but the one thing all these things have in common is that they all are happening on the screen. When the mind shifts from taking individual things in the field of awareness as the meditation object to taking the entire field of awareness itself as the object, it feels as if you have gone from watching the movie to looking at the screen. There is a pulling back, a sense that you are taking it all in at once.

As one continues observing the entire field of awareness hum along in high equanimity, a substantial increase in concentration occurs. You’ve already acquired a good deal of concentration in order to get this far, but now it jumps in power quite a bit. Part of the reason that this happens is that in higher equanimity the mind stops moving from one object to the next and begins to focus on a single object, the field of awareness itself. Please keep in mind that this happens all by itself. There is no special technique or effort involved. At this point very little effort is needed and all that is required is that you allow the process to happen.