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The X-Philes (2nd Revision)
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The X-Philes Number 1 (1995).iso
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batts2.doc
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1995-03-31
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BATTS2.DOC by stevev@miser.uoregon.edu [Steve VanDevender]
Date: 01 Mar 1993
[Note: There is a file called BATTS.DOC on Goodies Disk #8 which proposed
that battery drain is accelerated by improper orientation of the HP 48
relative to the direction of the ether wind. Here's another hypothesis
which is, uh, just as serious... -jkh-]
In article <1993Feb27.184413.12699@fuug.fi> an1060@anon.penet.fi writes:
I would like to know if the HP-48's power drain on the batteries is
significantly increased by more programs/data stored in RAM...
If so, then can someone quantify this relation??
We're glad you asked that, Mr. Mantell, ahem, we mean Mr. an1060!
As the chief research scientist at Speed Merchant Laboratories (a
wholly owned subsidiary of Speed Merchant, Inc.) I have been
studying this question for some time.
We at Speed Merchant use a variety of Hewlett-Packard equipment,
and HP 48SX calculators are standard issue to our research and
engineering staff. Corporate pennypinching has forced us to
ration batteries to our staff, and therefore finding ways to
extend battery life has become an issue of some concern. We have
run a series of experiments on this matter, and here present our
findings:
HP 48SX calculators were loaded with special memory patterns,
ranging from all zeros to all ones, leaving some available memory
to allow calculator operation, on calculators with no expansion
memory, one 128K memory card, or two 128K memory cards. The time
from installation of fresh batteries (we used Kodak Supralife
brand) until the low battery light came on was then recorded; due
to differing rates of use this time shows some variation which
was quite consistent.
HP 48SX with
32K 160K 288K
% of binary
1s in memory
0% 2160 hrs 2160 hrs 2160 hrs (+/- 720 hrs)
25% 90 days 90 days 90 days (+/- 30 days)
50% 12 weeks 12 weeks 12 weeks (+/- 4 weeks)
75% 3 months 3 months 3 months (+/- 1 month)
100% 0.25 years 0.25 years 0.25 years (+/- 0.83 years)
As you can see from the rapidly decreasing numbers, increasing
proportions of binary 1s in calculator memory makes a tremendous
difference in battery life. In general the 25-50% figures
represent typical usage, where memory is kept full or nearly full
assuming that stored data has a distribution of roughly half ones
and half zeros when expressed in binary form.
As a result of this research we are now working on ways to reduce
the number of binary 1s stored in HP 48 calculator memory using
various data compression techniques, but these will not be on the
market for some time. Until then, we can suggest a few methods
for reducing the number of 1s stored in your calculator's memory:
1. If a GROB contains more dark pixels that light pixels, use
the NEG command on it before storing it in memory, and use NEG
again just before placing it into the display. NEG on GROBs will
change dark pixels to light and light to dark; when used on a
mostly-dark GROB this will then reduce the number of 1 bits
needed to store it.
2. Use as few digits of precision as are needed in the problem
at hand, and use the RND or TRUNC commands before storing results
to truncate the excess digits and remove unneeded 1 bits.
3. Turn off unneeded display annunciators; besides requiring 1
bits in memory, activated annunciators also draw more power in
the display.
4. Clear the PICT and stack whenever the data in them is
unneeded.
5. Garbage collect frequently; don't wait until the heap is
exhausted. Make it a habit to do MEM DROP every few keystrokes.
We at Speed Merchant hope that this information has proven
useful. Once again, look for our soon-to-be announced HP 48
software package that will automatically minimize the number of 1
bits in memory and thereby improve your battery life in typical
usage from as little as 0.17 years to as much as 1440 hours!
Steve VanDevender
Chief Research Scientist
Speed Merchant Laboratories
a wholly owned subsidiary of Speed Merchant, Inc., manufacturers
of the Speed Merchant 5000 -- the only wheelchair with a roll
bar!
--
Steve VanDevender stevev@greylady.uoregon.edu
----------
Resp: 3 of 3 by rrd@hpfcso.FC.HP.COM [Ray Depew]
Date: 03 Mar 1993
Mr. VanDevender graciously provided us with battery usage numbers, but
he omitted the weight of all those binary 1's. (You know, the more 1's
in memory, the heavier the calculator weighs...) Perhaps Speed Merchant can
follow-up with a report on the comparative weights of different brands of
battery, and a recommendation on the optimum battery to use for
longest life, fullest RAM and lightest 48SX. Now *there's* an engineering
problem for you!
Regards
Ray Depew
Integrated Circuits Business Division
Hewlett Packard Co, Fort Collins, Colorado
rrd@hpfiqa.fc.hp.com