Accuracy of financial calculators 17BII, 19BII, and 30b

10212014, 06:53 PM
(This post was last modified: 10212014 09:58 PM by Jeff_Kearns.)
Post: #1




Accuracy of financial calculators 17BII, 19BII, and 30b
A review of the specifications for each of the HP17BII, HP19BII, and HP30b show that they have similar internal precision for intermediate calculations of 15 digits. The 17BII is somewhat vague on this and even states between 12 and 31 digits, depending on the calculation, although I can't find the reference now.
My question has to do with the determination of the 'nominal' interest rate for the following Canadian Mortgage calculation: N = 20 years (240 months) PV = $ 270,000 PMT = $ 1,497.41 per month FV = 0 What is the CI%/YR = ? I get some interesting results (showing ALL) as follows: HP30B: 3.018 7862 905 HP17BII: 3.018 7862 9301 HP19BII: 3.018 7862 86 Interestingly, the HP32Sii backsolves to the same answer as the 17BII, using this routine and an equation I=100x((1+i/200)^(16)1) for determining the Canadian mortgage factor. The HP33S, using the same routine as the HP32Sii, gives the same answer as the HP19BII. Which one is 'most' correct, considering they all have similar internal precision. The 30B has a builtin Canadian Mortgage mode, while the SOLVER routines for the 19BII and 17BII were taken from their respective manuals. Note that Canadian mortgages are compounded semiannually with payments made monthly. See this article for more information. Thanks! Jeff Kearns (Ottawa) 

10212014, 09:39 PM
Post: #2




RE: Accuracy of financial calculators 17BII, 19BII, and 30b
Have you considered to port your routine to the WP 34S (or its emulator) and let it run in double precision mode?
Marcus von Cube Wehrheim, Germany http://www.mvcsys.de http://wp34s.sf.net http://mvcsys.de/doc/basiccompare.html 

10212014, 09:54 PM
(This post was last modified: 10212014 10:12 PM by Jeff_Kearns.)
Post: #3




RE: Accuracy of financial calculators 17BII, 19BII, and 30b
(10212014 09:39 PM)Marcus von Cube Wrote: Have you considered to port your routine to the WP 34S (or its emulator) and let it run in double precision mode? Hi Marcus, I originally bought the 30B with the intention of converting it (repurposing it) to a WP 34S and never got around to it. I think I should go that route, or at least buy another one to do so, because I really do not like the user interface of the 30B with its 4level RPL stack and nonintuitive menus. Since I already own a 12C, 17BII, and 19BII, all of which I like and find easy to use, I have absolutely no need for a 30B as an engineer. I did however affix the plastic adhesive overlay that came with the 30B user's guide so maybe I should get another cheap 30B to repurpose as the new keyboard overlay won't likely adhere very well on the old one. I haven't gained much familiarity with the emulator yet and should investigate that and try porting the TVM routine and the CDN mortgage rate factor equation: I=100x((1+i/200)^(16)1) to see what it gives as a result. But does the 34S have an algebraic equation feature like the 32sii/33s/35s? Otherwise, it will have to be another program. In the meantime, I am hoping someone (maybe Gene?) can let me know what the 'correct' answer is to 13 significant digits. I am still trying to figure out which model is the most accurate. Cheers, Jeff K 

10222014, 05:16 AM
Post: #4




RE: Accuracy of financial calculators 17BII, 19BII, and 30b
HP200LX TVM Application: 3.018 7862 9049 9193


10222014, 04:19 PM
Post: #5




RE: Accuracy of financial calculators 17BII, 19BII, and 30b
(10222014 05:16 AM)Gerson W. Barbosa Wrote: HP200LX TVM Application: 3.018 7862 9049 9193 Thanks Gerson. That raises the question: "Why is the 30B more accurate than the 19BII, since they both use 15 digits internal precision?"  Jeff Kearns (Ottawa) BTW (OffTopic but I wanted to share): Today marks the first time ever that shots were fired in anger within the grounds of our Parliament Buildings in Ottawa. A sad day indeed in Canada. Breaking news at the moment... 

10222014, 04:37 PM
Post: #6




RE: Accuracy of financial calculators 17BII, 19BII, and 30b
(10222014 04:19 PM)Jeff_Kearns Wrote:(10222014 05:16 AM)Gerson W. Barbosa Wrote: HP200LX TVM Application: 3.018 7862 9049 9193 Since the hp30b has Canadian Mortgage builtin all calculations are carried out to 15 digits before the final rounding its result should be more accurate, I think. I don't know how this is done on the other calculator you've tried though. Starting at page 1417 of the HP 200LX User's Guide there's an example on Canadian Mortgages. Tuned to CNN right now. Really sorry about the sad news. Gerson. 

10222014, 07:04 PM
(This post was last modified: 10222014 07:22 PM by Werner.)
Post: #7




RE: Accuracy of financial calculators 17BII, 19BII, and 30b
Using my TVM program for the 42S, I find that the monthly rate is
i% = 2.49997833318e1 To get the Canadian annual rate, you have to calculate c% = ((1 + i%/100)^6  1)*200 If you do that using ^, you get the 19BII answer. If you calculate c% using LN1+X and E^X1 as c% = E^X1(LN1+X(i%/100)*6))*200 you get the 30B answer, exactly. All this using 12 digits only. The 30B answer is correct to 12 digits, the others probably do not use 15 digits throughout.. Werner 

10222014, 07:17 PM
Post: #8




RE: Accuracy of financial calculators 17BII, 19BII, and 30b
I don't have or know the "exact" answer, but in nearly all situations, go with the 30b. It has the accuracy above other HP financial models.


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