@acer I take your points.  It turns out that the Worksheet is arranged mostly as a collection of procedures, with two sections at the beginning.  I can perform the tests in the first section and simply surround the second section with an if ... end if

So actually much easier than I thought.

@acer Thank you for your explanation.  Yes, I am using Evaluate-->Execute Worksheet.  I guess it is the way that Maple is designed which makes this impossible.  In all the languages that I have come across (admittedly not that many) it is possible to cancel further execution of code programmatically.  But here is a thought ... or two

If I had a "launcher" worksheet whose sole purpose was to launch or start evaluation of the main worksheet, could perhaps the main worksheet perform the checks and return to the launcher if the checks failed?

Or, have the launcher perform the checks and only invoke the main worksheet if the checks passed?

@Scot Gould The title says it all - error does not prevent further execution

@dharr Following your advice, I can now tab from item to item. You stated earlier

You can't tab when the cursor is in a text box, but you can if it is not. Put the cursor to the left of the first text box and then try it. It tabs through the cells with txt boxes.

It is not necessary to place the cursor to the left of the text box.  It is still far from satisfactory however, because you still have to click inside the text box before you can edit its contents.  That really is ... a pain.

@acer Thanks for your suggestion.  I can see a couple of drawbacks with this approach, one of which you have mentioned (controlling the numeric formatting of the display).  The other drawback, from my point of view, is that these values are going to be used in a calculation.  It is much easier to associate a variable (e.g. Ka) with the contents of a TextArea named ta_Ka than to have to retrieve the required value by referencing a cell in a matrix by row and column.

@dharr 

 I don't find that tab creates a new line.

Working from the version of TextAreaPN.mw which you posted on 24th December this is what I get:

I hope the images are self-explanatory.  The last two images show the behaviour when the column is made wider. Anyway, I think we have pretty much exhausted what we can do with TextAreas, so thanks again for your time and help.

@dharr Not your help or examples, quite the opposite.

The title reflects the fact that I regard this use of TextAreas for numeric input as a poor substitute for a proper numeric entry control - alignment and cursor behaviour in a TextArea are quite different from what I would expect in a proper numeric entry control.

You can't tab when the cursor is in a text box, but you can if it is not. Put the cursor to the left of the first text box and then try it. It tabs through the cells with txt boxes.

If I have entered data in the first text box, how do I then put the cursor to the left of the text box without using the mouse? And when I did use the mouse to place the cursor to the left of the text box and pressed TAB, a new line was created - the cursor did not move to the next cell.  Is there something I am missing here?

Many thanks, once again.

Afterthought - perhaps I should be thinking about a Maplet solution?

Thank you, again.  Your code was very helpful and I have attached something of mine based on your example.  I wonder if you could comment on whether my effort could be improved (it's only a few lines)?  I would be grateful.

There are a couple of things I am not happy with:

1. Numeric values do not look like numeric values (i.e. not right-aligned etc)

2.The only way I could find to format the numeric value was using evalf 

3. I do not seem to be able to move from one TextArea to another using either the ENTER or TAB keys (I do have Tab Navigation checked on).

I may not be around for a couple of days so, in the meantime, I send you Season's Greetings.

(I will probably check back here later but might not respond until after the holiday)

TextAreaPN.mw

@dharr One of those pesky "gotchas" again ...

@Rouben Rostamian  Thank you.  I was not aware of plotsetup (I am very new to Maple) and I am sure that will come in very useful

@acer Thank you. By "inline plot component", you can see what I meant in the V16 worksheet attached.

The V17 worksheet is the one I had the problem with and the V18 worksheet is after my "fix"

V16_Calculation_of_pH_from_known_values_of_Vb_(Document)_ac4.mw

V17_Calculation_of_pH_from_known_values_of_Vb_(Document)_ac4.mw

V18_Calculation_of_pH_from_known_values_of_Vb_(Document)_ac4.mw

@dharr I see that now - thanks for the heads-up

I deleted the plot from the table.  The document then contained no plots.  I then inserted a new plot which was automatically named Plot0 and afer Execute Worksheet everything was fine.  Also, now when I right-click on the plot there is a Component  option

This is what I am seeing when I right-click on the plot

There is no component properties option (I had already looked for that)

@Joe Riel  Thank you for your reply and suggestion.  I'll go with that and see how I get on.

Thanks again!