ENG display mode on HP-15C

[Pekis]

Hello,

I was very disappointed to discover that, on the HP-15C, in ENG 0 mode, for example:

the value (100 * PI), ie +/- 314.159265354 is shown as 300 E0 !
I believed it would have displayed 314 E0

the value (PI / 100 000), ie +/- 0.0000314159265354 is shown as 30 E-6 !
I believed it would have displayed 31 E-6

I had not read the owner's handbook as for this aspect before but anyway, it doesn't seem logical for me ... See also the old thread on this forum ...

What do you think now in 2024 ?

Thanks

[Joe Horn]

"ENG n" mode displays n+1 significant digits of the mantissa. Therefore, ENG 0 mode displays only the first significant digit of the mantissa (rounded up when necessary). Thus pi times 100 in ENG 0 mode is properly displayed as 300 with an exponent of 00. This is true on all HP calculators (I'm pretty sure).

[Pekis]

OK, but if we talk about, for example, a precise calculated length of 178 mm, you cannot proudly announce 200 E-3 as if it were near of 200 mm !

[RPNerd]

(08-22-2024 12:26 PM)Pekis Wrote:  OK, but if we talk about, for example, a precise calculated length of 178 mm, you cannot proudly announce 200 E-3 as if it were near of 200 mm !

If you're presenting "a precise calculated length" then you should be using more than one significant digit!

[Pekis]

The significant digits are already present in the calculated number (178 in my example).

I see the ENG display as a special "Unit" display (E-3 in my example are mm); After the unit digits come the decimals but the unit digits must first be displayed without rounding if possible !

So we have 178 mm, and that number can be displayed ... who would want to see 200 ?

[KeithB]

"So we have 178 mm, and that number can be displayed ... who would want to see 200 ? "

No one, but what should it do if you enter ENG 0? Give an error? Seems like a waste of ROM to arbitrarily limit folks choices. What should the minimum be? 3? 2? 4?

[RPNerd]

(08-22-2024 01:31 PM)Pekis Wrote:  The significant digits are already present in the calculated number (178 in my example).

Correct. And there are three of them, not one.

[Pekis]

(08-22-2024 01:40 PM)KeithB Wrote:  "So we have 178 mm, and that number can be displayed ... who would want to see 200 ? "

No one, but what should it do if you enter ENG 0? Give an error? Seems like a waste of ROM to arbitrarily limit folks choices. What should the minimum be? 3? 2? 4?

It was though much more simple to do something similar to SCI and FIX, while adjusting exponent and decimals, and so not mixing significant digits with ENG and decimals like FIX and SCI...

[Craig Bladow]

I never use anything less than ENG 4 as that is what works best for me in most cases.

[RPNerd]

(08-22-2024 03:29 PM)Pekis Wrote:  It was though much more simple to do something similar to SCI and FIX, while adjusting exponent and decimals, and so not mixing significant digits with ENG and decimals like FIX and SCI...

That is kind of what it does.

FIX n shows n digits to the right of the decimal point.

SCI n shows n digits to the right of the decimal point in the mantissa part.

ENG n does the same thing as SCI n but adds zeroes as needed while adjusting the exponent to be a multiple of 3.

178 in SCI 0 would be: 2. 02

To get that in ENG 0 and have a mantissa between 1 and 1000 (excluded) you need to take 2 off the exponent and insert 2 zeroes before the decimal: 200. 00

[Pekis]

And my old Sharp EL-5103, in ENG 0, displays:
178 E-3 for 0,178
31 E-6 for Pi/100 000
314 E0 for Pi*100

Why, HP, why ?

[Steve Simpkin]

Interestingly enough, the first HP model to incorporate the ENG display option, the HP-25, always displayed at least 3 significant digits of the value. For example, when set to ENG 0, the value (100 * PI) is shown as 314 E0. All other models after the HP-25 that have the ENG display option show 300 E0.

From the HP-25 User's Handbook:
"Engineering notation is selected by pressing f [ENG] followed by a number key. In engineering notation, the first three digits are always present, and the number key specifies the number of additional digits displayed after the first three."

From the HP-29C/19C User's Handbook:
"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 additional significant digits to which the display is rounded."

It seems HP had a change of heart after the HP-25.

[AnnoyedOne]

(08-22-2024 04:42 PM)Steve Simpkin Wrote:  It seems HP had a change of heart after the HP-25.

The number of digits after the decimal point vs significant digits. And zero (not 1) based as well. The horror ;-)

[Pekis]

Quote:ENG n does the same thing as SCI n but adds zeroes as needed while adjusting the exponent to be a multiple of 3.

178 in SCI 0 would be: 2. 02

To get that in ENG 0 and have a mantissa between 1 and 1000 (excluded) you need to take 2 off the exponent and insert 2 zeroes before the decimal: 200. 00

The BIG problem with that insertion is that it makes you believe that 200 E0 is the result of rounding to the last digit (coming from 199.5 E0, or 200.4 E0, ...), which is not the case !

And there's no problem with in SCI 0 (2 E2) because 2 comes actually from rounding 1.78 E2 to 0 decimals ...

[brouhaha]

(08-22-2024 01:31 PM)Pekis Wrote:  So we have 178 mm, and that number can be displayed ... who would want to see 200 ?

The person thar told their calculator that they only wanted one significant digit, by using ENG 0.

Like SCI n, what ENG n controls is setting the number of significant digits displayed to n+1. Don't like that? Don't use ENG 0. I usually use ENG 3.

[AndiGer]

From the HP-67 manual, p. 46:
Notice that rounding can occur to the left of the decimal point, as in the case of ENG-0 specified above.

[RPNerd]

(08-22-2024 07:33 PM)Pekis Wrote:  The BIG problem with that insertion is that it makes you believe that 200 E0 is the result of rounding to the last digit (coming from 199.5 E0, or 200.4 E0, ...), which is not the case !

Like any form of computer, the calculator does what you tell it to do, which is not necessarily what you want it to do. By using ENG 0 you are telling the calculator that you don't want any digits after the mantissa's decimal point and that's what you're being given. If that's not what you want then you have to tell the calculator to give you something different.

Remember, 178 is stored internally as 1.78×10². The mantissa is 1.78. With no digits after the decimal point, it's going to get rounded up to 2 and ENG notation only affects how that number is being displayed.

[AnnoyedOne]

From p59 of the HP-15C Owner's Handbook (November 1985, Rev. G)

Quote:Engineering Notation Display

[ENG] (engineering) format displays numbers in an engineering
notation format in a manner similar to [SCI], except:

* In engineering notation, the first significant digit is always
present in the display. The number you key in after [f] [ENG]
specifies the number of additional digits to which you want to
round the display.

* Engineering notation shows all exponents in multiples of
three.

So [ENG] 0 does exactly what the manual says As RPNerd said that may not be what one thinks that it should do.

A1

PS: The HP-15C LE and CE manuals I have say the exact same thing.