Here are some blocks to take an Instant and back it up one day ...
backup_one_day.aia (1.7 KB)
So yes, you can indeed run time backwards using the Clock.
Since your app does not run any alarms or metronomes, you only need one Clock component to gain access to blocks that manipulate time values.
Thanks for all the replies 
I understand my "save" blocks are correct.
...this was because I corrected the image and forgot to correct "DateTime", ...it's all right.
With this setting, will the new Namespace be created automatically the next day? ...and the previous Namespace remains archived?
...interesting, but it is sufficient that I give the user only one option: all readings by clicking the List button.
The user can save his data without looking at the table every time the reading session ends. He looks at the table mainly when he wants to compare various readings.
But maybe this solution can be useful when I will need to recall namespaces with datepicker? I don't know how to do it yet.
Now I think it's time to build the table, ...without extensions.
I could assume a maximum of readings per day: 50
What is best to do:
Here, you can have multiple keys for multiple days, and day will be refreing to specifc table - list of lists for the multiple readings. Your current approach is correct but for me it looks Scattered not united. In a day user can save multiple readings, just clicking New-Reading, that will open a form to enter corresponding reading data and save. That reading will be saved along with the existing reading of that day only.
I have not paid any attentation to data-display logic, table-view, list-view, etc.
Yes,
Because they are separate files, they don't take up any RAM until you need to read them for export or display.
Performance-wise, this allows for fast update at constant speed, eliminating ever longer packing/unpacking delays from TinyDB that would occur if all the data stayed in a single TinyDB nameSpace file.
To display your data, you would need to build a table (list of lists) with your readings, one reading per row. I don't recommend displaying it all at once, unless you have an appetite for Javascript and html like in this approach: App Inventor Tutorials and Examples: Dynamic Table Layout | Pura Vida Apps from FAQ Section: Charts and Graphs
I personally favor using a small screen-sized fixed window of Horizontal Arrangements stacked in a Vertical Arrangement, with a thin vertical Canvas on the side for scrolling, and a global variable OFFSET (default 0) to hold how far down the aforesaid table is the section you are showing in the window.
I need sample data to make a demo of how to do this.
Can you gather a table of your readings (12 should be enough) and upload a csv file?
Oh, nice idea, but I have a feeling that it is not suitable for using my app.
What happens here is:
The user feels his pulse with his three fingers and detects various perceptions. Then he starts the app and selects the buttons that correspond to his perceptions (he collects one-reading data). Finally he saves the data and can close the app or go to see the table.
Some time later, he sits down again to feel his pulse, again collects the data (perceptions) by clicking the buttons and saves the next reading session.
In one day he can do from 0 to 20 readings, or more. It depends on how much he wants to practice in order to become an expert in the pulse-reading technique.
Data collection must be very fast and intuitive, that's why I use buttons instead of the form.
However your idea can be useful for something else. Every contribution is precious
I love the simplicity of this way of storage.
When the user goes to the table by clicking List button, he must see the current day in the Datepicker calendar and all the readings done on that day displayed in the table.
I have already tried to apply that Dynamic Table with Javascript and prefer to avoid it.
My appetite goes for the Arrangements
This is a possible quantity and distribution of data:
I have merged Time and Activity display to optimize space on the screen.
Even though we have the date appearing in the Datepicker, initially I kept the date in Day&Time column thinking about export, but for now we can try this solution.
Anyway I would like to keep the storage with Date and Time and also separate it from the Activity. Only in the visualization I would do as in the attached table.
...so this is my table with labels in Horizontal Arrangements 
I was able to feed the table with the data saved in Day namespace, but in a very rudimentary way. Obviously it cannot work for 50 table rows.
Nadi_05.aia (955.8 KB)
How can I improve the blocks and create the procedure to generalize feeding of labels of one row and apply it to any row?
In anticipation of your (and others) future need to scroll through a display of customized table rows, I created this sample:
This sample lets you scroll through hundreds of rows.
Regarding your blocks, I see a big red triangle of text replacement blocks where you steamroll a table into a text then try to pick out the resultant markup (",) characters by text replacement. For more customized control over table cell formatting, consider using the JOIN With Separator (\n or "," or " " or \t) block for your list to text conversion.
A table to text conversion might require 2 passes, building rows then piling them up with \n.
There is a table to csv conversion block that's even simpler.
I used the Join with separator block, but there are still segments to remove.
You remember that I am using milliseconds tags, I do not convert table to text.
Hi Ram
I will try this solution tomorrow,
...but there will be 50 rows, will I have to make 50 lists?
Mean, 50 * 6 = 300 Labels!
Yes, this is how you can refer label using anyComponent, since you cannot provide label names dynamically.
You don't need 50 lists.
You need a table that can expand to 50 rows.
Here's how to get such a table.
(Displaying a table has many solutions in AI2, divided into 3 schools of thought:)
You decide.
Abraham, I did not understand your corrections, can you explain better?
I intend to proceed with the fixed rows as I have set.
So what's your solution?
...unfortunately it doesn't work
it shows the same error warning as before
