Thank you for the quick support. Appearently I made the same mistake again and again: Forgetting the declarations of assumptions before using simplify.

Thank you also for the hints regarding the proper use of the MaplePrimes editor.

I understand, but how can I generate those grey-shaded boxes with Maple code which are used in all the MaplePrimes discussions (like in this one)? Sorry for my stupid question.

I understand. However, wouldn`t I run into the same trouble if I assign the constant explicitly and there is already another assigment for the same letter in my worksheet? I do not really see the advantage....

Yes, I can assign any name I want but one of the advantages of scientific constants is that the same notation is used in any textbook or publication, at least to my knowledge. Again, I do not see the advantage, but this is just my opinion of course.

Anyhow, I got it. But please explain why uneval quotes should be used. I must confess that because I am using Maple only occasionally I permanently get overwhelmed by the myriads of programming commands and possibilities.

@Markiyan Hirnyk The answer of pagan suggests to force the units. I mentioned that I do not want to use that method but that I am looking for a way that Maple does apply the correct units automatically.

I have noticed that many answers in this forum are focusing on solving a problem (which is absolutely ok!) but are forgetting to explain the mistake or the misconception causing the problem of the questioner. That is a real pity because then the questioner does not learn how to avoid his problem the next time.

I think I have found the reason for the behaviour of Maple in my case. As long as the independent variable is not defined it has no unit. My misconception was the assumption that if I assign a plotting range with units to the variable that the plot procedure processes also the unit and thus provides the correct unit for the labels of both axis. However this is only true for the axis of the independent variable (the x-axis) but not for the dependent variable (y-axis). To get it right for the y-axis I have to tell Maple the unit of the independent variable in the expression, as I did in the following example.

However I still don't know why the dependent variable is omitted on the y-axis. It should read "A m³" and not "m³".

@Markiyan Hirnyk 

I browsed through the list but was not able to find an answer which matches my case. I don't get error messages like in the other cases, I only get a wrong dimension for the y-axis and I can't understand why. I also do not want to force the dimension labellling of the axis as proposed in several answers of the list.

@acer Thank you but in spite of the complexity of your workaround I will simply omit units for angles. I will tell the users of my worksheet to enter numbers in degrees and re-calculate those to rad. That works perfectly, like in the old days before units were supported by Mathcad.

By the way I talked to some mathematicians and their opinion was that the way Maple has implemented the radian unit is simply wrong. Radian = arclength / arcradius with the unit m/m = 1. There is no unit m(radius). By using such a unit Maple is inventing a new dimension. I cannot imagine any mathematical or physical problem which would benefit from such a definition.

@Samir Khan 

The worksheet was sent to the address you have provided. I have mentioned your name in the subject line.

@Thomas Richard I have just uploaded the file angles2.mw

@Samir Khan 

I am doing radar systems design. Our basic equation is the radar equation which mixes many units including deg, m, W, Hz, m/s etc. I am well aware that Maple and Mathcad are completely different products and I am trying to do a fair evaluation. However units are an extremely important validation tool for engineering worksheets. We cannot omit them. (I should also mention that the results of this evaluation may be the basis of a decision to switch from Mathcad to Maple for all of us).

@Thomas Richard 

Usually the other variables in an engineering equation are also scaled with units. unit_free does not help because it removes all units:

The result should be 3141.59m.

I tried to remove only the angle unit but now something strange happens:

THETA should be pi/2 and not 90. In the first example unit_free has converted degrees to radians, but not in the second example. I can't see the difference.

@Samir Khan 

Yes, I am trying to convert a Mathcad worksheet to Maple. Since I am using Maple for the first time this is more or less a big practice although I really need this worksheet. I think that Maple can do everything which Mathcad can (and much much more!) but in Mathcad it is much easier, mostly because the sheer number of functions and features in Mathcad is much smaller, and because engineers seem to be the target customers of Mathcad (I have just read the discussions about phasors :)  ).

This unit problem is solved for me, but it is no problem to post a Mathcad worksheet in case of other questions. As a matter of fact I am currently writing a new question, on the use of angle units.

@acer

Thank you very much!

By the way is there any kind of vocabulary for naming quotes in Maple? I am using a German keyboard. What you are calling  "single-right quote" or "forward quote" is the "apostroph" or "single quote" on this keyboard. Here are all single quote which I can access without calling ASCII codes:

` back quote

´ forward quote (does not work, CTRL+ALT+ ` on a US keyboard!)

' single quote (works)

@acer You got the point. I left the colon intentionally in order to understand the difference between := and = . Thank you for the explanation.

I was using Mathcad since almost 30 years and am now considering switching to Maple. To be abel to work with units is one of the big advantages of Mathcad (15, not Prime) if you are an engineer.