Depreciation - different results on HP30b and on paper
03-12-2021, 12:05 AM (This post was last modified: 03-12-2021 12:11 AM by FabioBrasil.)
Post: #1
 FabioBrasil Junior Member Posts: 14 Joined: Dec 2020
Depreciation - different results on HP30b and on paper
Hello.
I come again to kindly ask for help from you who know a lot about HP. I cannot make the result of the calculation of decreasing depreciation (DecBal) provide the same result on the HP30b calculator and on paper.

The problem consists of the following:
- Cost (Czero)= $25000 - Salvage =$ 5000
- Life = 15 years
- Factor =10.174%

On paper D (n) = Czero * (1- Factor) ^ n
in year 1 I have 22,456.50
in year 3 I have 18,119.49
in year 6 I have 13,132.64
in year 12 I have 6,898.65
(n = year use as Factor 10.174%)

On the HP30b calculator (use as Factor 10.174%):
in year 1 I have 24,830.70 (R.Book)
in year 3 I have 24,494.94
in year 6 I have 24,000.08
in year 12 I have 23,040.16
Where am I going wrong? I couldn't get the answer on the Learning Modules.

Thanks!
03-12-2021, 05:13 PM
Post: #2
 SlideRule Senior Member Posts: 1,368 Joined: Dec 2013
RE: Depreciation - different results on HP30b and on paper
Methods of Depreciation: Formulas, Problems, and Solutions

Straight Line Method

Declining Balance Method
Declining Balance Method is sometimes called the Constant-Percentage Method or the Matheson formula. The assumption in this depreciation method is that the annual cost of depreciation is the fixed percentage (1 - K) of the Book Value (BV) at the beginning of the year.
Annual Rate of Depreciation(K): SV = FC (1 - K)n

source:Depreciation Methods in Engineering Economics

Any SME's with the formula/equation deployed in the HP-30B ?

BEST!
SlideRule
03-12-2021, 05:33 PM
Post: #3
 Werner Senior Member Posts: 802 Joined: Dec 2013
RE: Depreciation - different results on HP30b and on paper
(25000 - 5000)*(1 - 10.174/1200) + 5000 = 24830.43
So it would seem it works per month i.o. per year.
Werner

41CV†,42S,48GX,49G,DM42,DM41X,17BII,15CE
03-12-2021, 05:47 PM
Post: #4
 toml_12953 Senior Member Posts: 2,040 Joined: Dec 2013
RE: Depreciation - different results on HP30b and on paper
(03-12-2021 12:05 AM)FabioBrasil Wrote:  Hello.
I come again to kindly ask for help from you who know a lot about HP. I cannot make the result of the calculation of decreasing depreciation (DecBal) provide the same result on the HP30b calculator and on paper.

The problem consists of the following:
- Cost (Czero)= $25000 - Salvage =$ 5000
- Life = 15 years
- Factor =10.174%

On paper D (n) = Czero * (1- Factor) ^ n
in year 1 I have 22,456.50
in year 3 I have 18,119.49
in year 6 I have 13,132.64
in year 12 I have 6,898.65
(n = year use as Factor 10.174%)

On the HP30b calculator (use as Factor 10.174%):
in year 1 I have 24,830.70 (R.Book)
in year 3 I have 24,494.94
in year 6 I have 24,000.08
in year 12 I have 23,040.16
Where am I going wrong? I couldn't get the answer on the Learning Modules.

Thanks!
It looks like your paper version is correct.

Code:
 DECLARE FUNCTION D INPUT PROMPT "Cost? ":Czero INPUT PROMPT "Salvage? ":Salvage INPUT PROMPT "Factor? ":Factor LET n = 1 DO UNTIL D(n) <= Salvage    PRINT n,USING$("$##,###.##",D(n))    LET n = n + 1 LOOP FUNCTION D(n)    LET D=Czero*(1-Factor)^n END FUNCTION END Cost? 25000 Salvage? 5000 Factor? .10174  1                      $22,456.50 2$20,171.78  3                      $18,119.50 4$16,276.02  5                      $14,620.10 6$13,132.65  7                      $11,796.53 8$10,596.35  9                      $9,518.28 10$ 8,549.89  11                     $7,680.03 12$ 6,898.66  13                     $6,196.79 14$ 5,566.33  15                     \$ 5,000.01

Tom L
Cui bono?
03-12-2021, 06:50 PM
Post: #5
 SlideRule Senior Member Posts: 1,368 Joined: Dec 2013
RE: Depreciation - different results on HP30b and on paper
FabioBrasil

BEST!
SlideRule
03-13-2021, 12:32 AM (This post was last modified: 03-13-2021 12:33 AM by FabioBrasil.)
Post: #6
 FabioBrasil Junior Member Posts: 14 Joined: Dec 2020
RE: Depreciação - resultados diferentes no HP30b e no papel
Thank you for your help! It is good to have good people.
03-13-2021, 04:25 AM (This post was last modified: 03-13-2021 05:15 AM by paul0207.)
Post: #7
 paul0207 Junior Member Posts: 17 Joined: May 2014
RE: Depreciation - different results on HP30b and on paper
Fabio,
This is how I get the same answer on the HP12c (I don't have an hp30b to check it out, sorry).
25000 -> PV
15 -> n
152.61 -> i (that is 10.174 * 15)
Both PMT and FV = 0.
Then 1 DB yields
2543.50
x<-->y

Summing up, try i=152.61 (i*n) on the hp30b for the Declining Balance method.

Hope this helps,

Paul
03-13-2021, 12:15 PM
Post: #8
 Albert Chan Senior Member Posts: 2,235 Joined: Jul 2018
RE: Depreciation - different results on HP30b and on paper
(03-13-2021 04:25 AM)paul0207 Wrote:  Summing up, try i=152.61 (i*n) on the hp30b for the Declining Balance method.

Yes! This is from HP-12C Appendix D, formula used for DecBal:

DPNj = RBVj-1 * FACT / (100L), for j = 1, 2, ..., L

We can also consider DecBal as TVM problem, with negative interest rate:

10.174 [CHS] [I]
25000 [CHS] [PV]
0 [PMT]

Book values, for different years:

1 [N] [FV] ﻿ ﻿ ﻿ ﻿ ﻿ ﻿ → 22456.50
3 [N] [FV] ﻿ ﻿ ﻿ ﻿ ﻿ ﻿ → 18119.50
6 [N] [FV] ﻿ ﻿ ﻿ ﻿ ﻿ ﻿ → 13132.65
12 [N] [FV] ﻿ ﻿ ﻿ ﻿ ﻿ →﻿ ﻿ 6898.66
15 [N] [FV] ﻿ ﻿ ﻿ ﻿ ﻿ →﻿ ﻿ 5000.01

We can derive book value formula directly, by fitting the power law:

book_value / cost = (salvage / cost) ^ (years / life)

when exponent = 0, book_value = cost
when exponent = 1, book_value = salvage

For above example, we have:

book_value = 25000 * 0.2 ^ (years/15)
03-14-2021, 09:04 PM
Post: #9
 FabioBrasil Junior Member Posts: 14 Joined: Dec 2020
RE: Depreciação - resultados diferentes no HP30b e no papel
Paul0207, Thank you very much!
You solved the problem with Factor = rate * lifetime. In the Declining Balance mode (DecBal) this made me arrive at the same values of the exercise. Many, many thanks to all the colleagues who taught me a lot!

Paul0207, most things are the same on the HP12C and the HP30b. So much the same, that I use programs written for the HP12c on the HP30b with few modifications. And you don't need to apologize for anything, I appreciate your help!
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