PC1211, PC1250, etc. TVM

03302021, 04:58 PM
Post: #1




PC1211, PC1250, etc. TVM
In light of all the recent Sharp enthusiasm, here's my attempt at a TVM solver for the PC1211, and compatible models like the PC1250, and no doubt many others (and their corresponding Tandy/Radio Shack versions).
The math is based largely on the 17BII manual's formulas, this TVM program for serveral different HPs, and some of the mathematical notes found here. The PC1211 and PC1250 don't have hyperbolic functions for easy, accurate calculation of e^x1 for x close to zero, but using the infinite series for ln(1+x) does offer some accuracy improvement. Usage is fairly straightforward. On the PC1211, you'll need to switch to DEF mode. On other models like the PC1250, there's a dedicated DEF key that you press instead of Shift. Set B=1 for begin mode, otherwise set B=0. These are the key assignments  for storing variables, first enter the value into the display, then press the appropriate key: Shift Z: Store n Shift X: Store i% Shift C: Store PV Shift V: Store PMT Shift B: Store FV Shift A: Compute n Shift S: Compute i% Shift D: Compute PV Shift F: Compute PMT Shift G: Compute FV Code: 1 "Z":AREAD N Results are generally pretty good, and don't seem to differ by more than a few thousandths of a penny in the few sample problems that I tried. I'm not sure if the Sharps use binary rather than decimal, but I did notice that solving for PMT in a problem where FV=0, then immediately solving for FV could yield small nonzero values on the order of 1E5. 

03302021, 05:07 PM
Post: #2




RE: PC1211, PC1250, etc. TVM
Thanks for sharing!
(03302021 04:58 PM)Dave Britten Wrote: I'm not sure if the Sharps use binary rather than decimal, but I did notice that solving for PMT in a problem where FV=0, then immediately solving for FV could yield small nonzero values on the order of 1E5. FYI. SHARP pocket computers use 10 digits BCD to display values and store values in variables and 12 digits internally to evaluate expressions. For example (SQR is sqrt): SQR 2 * SQR 2 2 X=SQR 2 X*X 1.999999999 There is a small penalty to use variables to store (temporary) results. It is sometimes beneficial to "inline" expressions to preserve or increase accuracy.  Rob "I count on old friends"  HP 71B,PrimeTi VOY200,Nspire CXII CASCasio fxCG50...Sharp PCG850,E500,2500,1500,14xx,13xx,12xx... 

04012021, 04:44 PM
Post: #3




RE: PC1211, PC1250, etc. TVM
(03302021 05:07 PM)robve Wrote: Thanks for sharing! Good to know! Interestingly, I tested the same TVM program on the EL5500III that I received in the mail today (this model supports twocharacter variable names, so explicit * had to be inserted in most of the implied multiplications), and it seems to have better accuracy. Example: N=360 I=4.75/12 (3.958333333E01) PV=141000 FV=0 Solve for PMT, on both machines: PMT=735.5227446 Then immediately solve for FV without entering anything else. PC1250A (Tandy PC3): FV=3.731560805E05 EL5500III: FV=0. 

04012021, 05:50 PM
Post: #4




RE: PC1211, PC1250, etc. TVM
(04012021 04:44 PM)Dave Britten Wrote: Example: I also get FV=0 with a PC1350 with PMT=732.6227796 reported for DEFV. This value is also computed with the alternative 100105 lines. The SBASIC interpreter and the CPU on the EL5500III and PC1350 are (almost) the same, the forensics: http://www.rskey.org/~mwsebastian/miscprj/results.htm see also http://basic.hopto.org/basic/manual/basiccompare.pdf The BASIC of the PC1211 is an earlier S'BASIC. The PC1250 is derived from that early version, see: https://sharppocketcomputers.com/#basic  Rob "I count on old friends"  HP 71B,PrimeTi VOY200,Nspire CXII CASCasio fxCG50...Sharp PCG850,E500,2500,1500,14xx,13xx,12xx... 

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