ENG mode, n+1?

[Tim Wessman]

So I was just wondering why on the 48 series and onwards (maybe in earlier units too?) the ENG display mode actually seems to do n+1 and is mislabeled as "enter decimal places to display".

For example, on the 48-50, ENG 4 would show this:

123.456789: 123.46E0
1234.56789: 1.2346E3

and so on. So ENG 4 actually shows 5 digits and has nothing to do with "decimal places". What was the first place it started behaving like this? What is the reasoning behind the N+1 and why the mislabeling as "decimal places"?

[brouhaha]

(01-13-2014 10:32 PM)Tim Wessman Wrote:  So I was just wondering why on the 48 series and onwards (maybe in earlier units too?) the ENG display mode actually seems to do n+1 and is mislabeled as "enter decimal places to display".

For example, on the 48-50, ENG 4 would show this:

123.456789: 123.46E0
1234.56789: 1.2346E3

and so on. So ENG 4 actually shows 5 digits and has nothing to do with "decimal places". What was the first place it started behaving like this? What is the reasoning behind the N+1 and why the mislabeling as "decimal places"?

I think the rationale was for "ENG n" mode to show the same total number of digits as "SCI n" would show. AFAIK, this originated with the HP-25 in 1975.

The description may well be poor, but I think the behavior is desirable. I wouldn't want an "ENG 3" mode that resulted in 4, 5, or 6 significant digits displayed; I'm happy with it always showing four significant digits.

[Didier Lachieze]

(01-13-2014 10:32 PM)Tim Wessman Wrote:  For example, on the 48-50, ENG 4 would show this:

123.456789: 123.46E0
1234.56789: 1.2346E3

and so on. So ENG 4 actually shows 5 digits and has nothing to do with "decimal places". What was the first place it started behaving like this?

It's the same on my 41C. I think that the reasoning behind this is to display the same number of digits in SCI n and ENG n:

123.456789: 123.46 E00 in ENG 4
123.456789: 1.2346 E02 in SCI 4

From the 41C manual (http://www.greendyk.nl/hp41c-manual/index.php?p=34) :

Quote:Engineering notation is selected by pressing f ENG followed by a number key. The first significant digit is always present in the display, and the number key specifies the number of additionnal significant digits to which the display is rounded. The decimal point always appears in the display.

123.456789: 100. E00 in ENG 0
123.456789: 1. E02 in SCI 0

[Didier Lachieze]

I've checked the 48SX manual. It says page 59:

Quote:FIX, SCI, and ENG require a numerical argument:

• Fix mode requires the number of decimal places.
• Scientific mode requires the number of decimal places in the mantissa.
• Engineering mode requires the number of mantissa digits to be displayed after the first significant digit.
  

It seems these details have been lost starting with the 48g manual.

[RMollov]

(01-14-2014 12:06 AM)Didier Lachieze Wrote:  I've checked the 48SX manual. It says page 59:

Quote:FIX, SCI, and ENG require a numerical argument:

• Fix mode requires the number of decimal places.
• Scientific mode requires the number of decimal places in the mantissa.
• Engineering mode requires the number of mantissa digits to be displayed after the first significant digit.
  

It seems these details have been lost starting with the 48g manual.

HP48G manual, page 4-10:
"ENG" Sets the display mode to Engineering using the number on level 1 for the number of mantissa digits to be displayed after the first significant digit.

[walter b]

Tim,

It has always been this way AFAIK. This is to ensure a smooth transition to SCI.

d:-)

[Michael de Estrada]

Tim,

I think you are misinterpreting the setting and it is doing exactly what it says it does, namely showing at a maximum the number of digits after the decimal point as the setting. So, per your example with Eng 4,

123.456789 --> 123.46 E0 with 2 decimal places
1234.56789 --> 1.2346 E3 with 4 decimal places
12345.6789 --> 12.346 E3 with 3 decimal places
123456.789 --> 123.46 E3 with 2 decimal places
1234567.89 --> 1.2346 E6 with 4 decimal places

[Han]

(01-14-2014 03:03 AM)RMollov Wrote:  HP48G manual, page 4-10:
"ENG" Sets the display mode to Engineering using the number on level 1 for the number of mantissa digits to be displayed after the first significant digit.

I think this explains it almost right (emphasis on the word "after" is mine). Perhaps what is lacking is that engineering mode always uses powers of tens that are multiples of three since it is fairly common to separate the digits of a number into groups of 3 digits. So ENG 4 means display the number is such a way that only 4 digits appear AFTER the most significant digit once proper exponents have been accounted for. The placement of the decimal point is completely determined by the exponent.

[walter b]

(01-14-2014 06:28 AM)Han Wrote:  

(01-14-2014 03:03 AM)RMollov Wrote:  HP48G manual, page 4-10:
"ENG" Sets the display mode to Engineering using the number on level 1 for the number of mantissa digits to be displayed after the first significant digit.

I think this explains it almost right (emphasis on the word "after" is mine). Perhaps what is lacking is that engineering mode always uses powers of tens that are multiples of three since it is fairly common to separate the digits of a number into groups of 3 digits.

Emphasis added. As long as people use SI, those multiples of three perfectly match the common steps like k, M, G, T, etc. So the ENG format is the natural format for 99% of engineers on this planet.

d:-)

[Tim Wessman]

Interesting. I didn't realize that the behavior was so old. Thanks everyone that commented!

[Dieter]

(01-13-2014 10:32 PM)Tim Wessman Wrote:  So I was just wondering why on the 48 series and onwards (maybe in earlier units too?) the ENG display mode actually seems to do n+1 and is mislabeled as "enter decimal places to display".

All HP (and other) calculators I know of, when set to SCI n or ENG n, will display n+1 significant digits of the result. So both SCI 4 and ENG 4 show five mantissa digits. The difference only is the decimal marker that in ENG mode is placed so that the exponent is a multiple of three.

Dieter

[David Hayden]

A good way to explain it (or at least the way that I explain it in my own head) is that SCI n shows scientific notation with n digits after the decimal. ENG n is the same as SCI, except that the exponent is always a multiple of 3 and the decimal point moves to match.

Dave

[Neil Hamilton]

(01-14-2014 02:45 PM)Dieter Wrote:  All HP (and other) calculators I know of, when set to SCI n or ENG n, will display n+1 significant digits of the result. So both SCI 4 and ENG 4 show five mantissa digits. The difference only is the decimal marker that in ENG mode is placed so that the exponent is a multiple of three.

My HP25 does not follow this. From the manual: "...the number of additonal digits displayed after the first three" (HP's emphasis). I think that the 25 was the first to have ENG mode, IIRC. I am pretty sure the HP29C is the same as well, though the manual text is a wee bit more wordy.

So 12.345678 EEX 6 followed by f ENG 2 would display "12.346 06". Whereas f SCI 2 shows "1.23 07".

My HP11C displays as follows: "In engineering notation, the first significant digit is always present in the display. The number key you press after f ENG specified the number of additional significant digits to which you want the display to be rounded." Same examples on the 11C:

12.345678 EEX 6 f ENG 2 => "12.3 06"
f SCI 2 => "1.23 07"

I don't (currently) own anything in between but the change in ENG behaviour obviously happen in the intervening models.

[Michael de Estrada]

The curious thing is that I'm an engineer (retired) and yet I hardly ever found the need to use engineering mode on my calculators. The reason is that I always used the correct implicit units in my calculations to avoid huge whole numbers in my final results. I would use kips instead of pounds or megawatts instead of watts. If I did have to enter a large number, then I'd simply use scientific notation with whole numbers only. This way I'd avoid having to chase the decimal point around the display the way you do with standard notation.

[Dieter]

(01-16-2014 01:26 PM)Neil Hamilton Wrote:  My HP25 does not follow this.
...
So 12.345678 EEX 6 followed by f ENG 2 would display "12.346 06". Whereas f SCI 2 shows "1.23 07".

That's interesting. So the HP25 actually behaved differently? I do not have one at hand so I cannot try this myself.

(01-16-2014 01:26 PM)Neil Hamilton Wrote:  [HP25 and 11C]
I don't (currently) own anything in between but the change in ENG behaviour obviously happen in the intervening models.

The HP25 was introduced in 1975, followed by the HP67/97 with the usual n+1 behaviour in the next year. So if there was a change it must have happened within this short period, 1975/76.

Addendum:
I just checked the HP journal article from November 1975 where the new HP25 is mentioned. At the end of page 5 it says:

Quote:... Setting the HP-25 to engineering notation gives the answer as 50.0  -06 which is easy to read instantly as 50 microseconds. (...) If the answer above is multiplied by 10, it gives 500.  -06 or 50 microseconds. Multiplying again by 10 gives 5.00  -03 or five milliseconds.

This would mean that the HP25 did not behave differently in ENG mode, and it displayed the result like most other HPs.

?!?

Dieter

[Thomas Klemm]

Quote:it gives 500. -06 or 50 microseconds

ಠ_ಠ
Where is walter b when we need him?

I don't have an HP-25 but from using the emulator I assume that's a bug: ENG n is off 2 places displaying ENG n+2 instead.

Cheers
Thomas

Edit:

Quote: "...the number of additonal digits displayed after the first three" (HP's emphasis)

Not a bug then. Works as designed. I should have read Neil's post. But still sounds arbitrary. Why "after the first three"?

[walter b]

(01-17-2014 03:05 AM)Thomas Klemm Wrote:  

Quote:it gives 500. -06 or 50 microseconds

ಠ_ಠ
Where is walter b when we need him?

[Dieter]

(01-17-2014 03:05 AM)Thomas Klemm Wrote:  

Quote:it gives 500. -06 or 50 microseconds

Yes, of course 500.  -06 stands for 500 microseconds. #-)
My error, the HP Journal text is correct here.

But let's get back to the facts. Could someone with a "real" HP-25 please check how it works in ENG mode? Until then I assume it behaves as described in HP Journal, i.e. in the same way as at least most other HP calculators. The authors of the mentioned article did the microprogramming, so they should know how everything is supposed to work.

HP25 owners: now it's up to you.

Dieter

[Thomas Klemm]

(01-17-2014 08:05 PM)Dieter Wrote:  Until then I assume it behaves as described in HP Journal, i.e. in the same way as at least most other HP calculators.

What you may have missed is that the example given is using ENG 0. Thus it's not the same as with later models. That's what Neil was pointing out.

Cheers
Thomas

[Neil Hamilton]

(01-17-2014 08:05 PM)Dieter Wrote:  

(01-17-2014 03:05 AM)Thomas Klemm Wrote:  

Yes, of course 500.  -06 stands for 500 microseconds. #-)
My error, the HP Journal text is correct here.

But let's get back to the facts. Could someone with a "real" HP-25 please check how it works in ENG mode? Until then I assume it behaves as described in HP Journal, i.e. in the same way as at least most other HP calculators. The authors of the mentioned article did the microprogramming, so they should know how everything is supposed to work.

HP25 owners: now it's up to you.

Dieter

What I gave you was from my REAL HP25 and from the HP25 manual. I typed it into the 25 before I typed it into the message board.

Not sure what the Jounal says but I have the calculator in my hands...

As far as ENG 0 goes: 12.345678 EEX 6 f ENG 0 shows "12.3 06".