Plus42 Equations, Preview Release

[Ajaja]

BTW, HP calculators have some peculiarity with calculation of amortization when balance changes sign. At first, comparing results, I thought that Plus42 fails to calculate Interest parameter in AMORT program properly, but after some considerations I realized that HP-17b/19b/27s AMORT program does it mathematically wrong.
There is an example (look at "Interest"):
HP-17bII

Code:

I%YR=              10.00
PV=            10,000.00
PMT=             -514.14
P/YR=              12.00
END MODE

PMTS:1-12
INTEREST=        -756.34
PRINCIPAL=     -5,413.34
BALANCE=        4,586.66

PMTS:13-24
INTEREST=        -209.96
PRINCIPAL=     -5,980.18
BALANCE=       -1,393.52

PMTS:25-36
INTEREST=        -436.70
PRINCIPAL=     -6,606.38
BALANCE=       -7,999.90

Plus42:

Code:

I%YR=              10.00
PV=             10000.00
PMT=             -514.14
P/YR=              12.00
End Mode

PMTS:1-12
Interest=        -756.34
Principal=      -5413.34
Balance=         4586.66

PMTS:13-24
Interest=        -189.51
Principal=      -5980.17
Balance=        -1393.51

PMTS:25-36
Interest=         436.70
Principal=      -6606.38
Balance=        -7999.89