Confusion about Custom Units in MathCad Prime 2.0

[rschor]

I often use MathCad to write documents that contain "usable math". Right now, I'm writing a document that involves Image files, file sizes, transfer rates, etc. I want to create a unit "B" (or "Byte"), maybe define MB as a mega-byte, and so on. So I might say an image is 640B * 480 = 0.3072 MB.

What I'm trying to do is to create a unit that is like a "counter", such as the "degree" unit, that I can attach to a quantity and have it "stick" to the quantity as a label. Reading the Custom Units "Help", I'm pretty sure that if I can figure out how to create a Byte unit, I can figure out MegaByte. However, the "dB" example in the Help menu gives me a bit of pause because applying the dB "unit" causes the unit label itself to disappear! I'd want something like the following -- I type 640*480 B (attaching a Byte unit label) and get 307200 B (OK, so far). I then replace the unit B with the unit MB and have the result transform to 0.3072 MB.

I don't know if this is, indeed, possible in MathCad Prime 2.0. If it is, that's wonderful, and I'd love to know how to do it. If it is not (yet) possible, I'd like to suggest adding this functionality to MathCad, as it will make it even more flexible to those of us who use it to create documents that include useful math.

[ValeryOchkov]

We can use dB in Mathcad 15 thru the using prefix and postfix operators.

But we have not prefix and postfix operators in Prime

[AlanStevens]

You can set B:=1 and MB:= 10^6 B and label them as Unit from Labels menu. However, the unit does not 'stick' this way.

If you aren't interested in the money unit you can do the following:

This way the unit 'sticks' but you still have to change it to look like B or MB by hand.

Alan

[ValeryOchkov]

Or

kB=1024B (2^10)

MB=2^20B etc

[rschor]

Good point -- kB and MB can have different meaning depending on how you define "k" and "M". The Good News is the definition is right out there, unambiguous (which is more than I can say for, say, Windows -- when they specify file size, which "Mega" do they mean? Note that this is not a serious question -- if I really need to know, you can bet I'll look it up ...).

BS

[StuartBruff]

There is some confusion about what MB and GB means, and it depends upon context. RAM tends to be measured in powers of 2, hard drives however tend to measured in mixed format. I believe there has been some litigation as a result of consumers not realizing that their "300 GB" disk is actually less than the equivalent in RAM.

The IEC, and various other organizations, now standardize on k, M, G etc to be the ISO (SI) multipliers with the terms Ki (kibi), Mi (mibi) and Gi (gibi) acting as their power of 2 "equivalents". I am seeing this notation more frequently on products.

Have a look at Wiki - http://en.wikipedia.org/wiki/Gigabyte

or http://forums.seagate.com/stx/board/crawl_message?board.id=ata_drives&message.id=25537

Stuart

[rschor]

I like this idea. Perhaps it could be generalized by having a "blank unit" defined (instead of "Money") explicitly so users really could define their own units that "stick". Anything you wanted to define you'd first define as a Blank Unit, then use it whereever it was appropriate. I don't see any reason you could have multiple "counters" such as Bytes or Chickens being defined as a Blank Unit without conflicts. If I'm talking about computer memory, I'll use the unit Bytes (which is a Blank Unit); if I'm talking about the contents of my Hen House, I'll use the unit Chickens (also a Blank Unit).

So I'll amend my previous suggestion to PTC -- consider adding a "Blank Unit" that users can customize for their needs.

[ValeryOchkov]

I have used cd for $ (money) in Mathcad 11, we now use $ for Byte.

Yes, we need a blank (three) dimension(s) in Mathcad!

[StuartBruff]

<pedant>What we need is the ability for the user to define their own System of Quantities as defined in the VIM (International vocabulary of metrology).

This should allow the user whatever quantities are necessary to effect their model and to define the necessary units and relationships (to ensure that simplification works). It should allow the user to add quantities and units in such a way that they appear in the 'Insert' and 'Options' dialogs. All additions and changes should be recorded within the worksheet and not be implemented via direct modification of Mathcad system files (eg, mpl) - the latter approach is not generally portable.

As with many things, I see little point in specifying some arbitrary upper limit (eg,3) when it is probably just as easy to design and implement a generic system that will be limited by system constraints and resources rather than what people think is "reasonable" (we had a similar discussion about limiting the number of dimensions in a multi-dimensional array capability - it is just as easy to allow what the system will take as to try and apply limits - been there, done that, printed the T-shirt!)

Stuart