HP 12C - 12c Platinum -- VAT amount, NET, GROSS

[Dr_Who2]

Hello everyone,

I am new to this forum and here comes a warm greeting to all members.

As for my person, I am no mathematician nor an engineer.
If I have to do any calculation in the field, it is related to financial problems or tasks.

To make a long story short, I obtained a new HP-12C Platinum mostly for nostalgic reasons and since I was curious about the so called RPN method.
As luck would have it, I also received in addition a pre-owned HP-12C as a gift.

Now, recently I had to calculate net and VAT-amount from gross amount given to me in a hand written list. Knowing the tax rate (19%), I thought this to be an easy out of the box task.
I soon figured, it is not.

The underlying math is no problem.
Since I received a quiet long list, I wished the HP-12CP and HP 12-C respectively had a key to deduct and/or add the tax instantly.

I found this entry in the old archive Forum: Posted by Kalevipoeg on 26 Nov 2005

This helped a lot.
While the approach from Kalevipoeg helps to deduct the tax, it naturally does not work vice versa. The approach is nice, since once the program is keyed in, it takes few key strokes to get the desired result.

I found the Message #3 by tony(nz) in the above thread most helpful, since it works both ways.
This is to say, if i, n (1) and PMT (0) are given, you can either enter the net amount (PV) or the gross amount (FV).

The approach from Tony really solved the problem at hand with the HP-12CP.
The procedure goes as follows:

0 -> PMT
1 -> n
19 -> i
238 -> FV
Press PV for net amount
= -200

This also works vice versa

0 -> PMT
1 -> n
19 -> i
-200 -> PV
Press FV for gross amount
= 238

Now, with this you get either the net value or the gross value. If one has a long list with gross values, you simply once key in n, i and PMT and you are ready to go as long as you wish.
What you miss, is probably the VAT amount.

On the HP-12CP this is simply done by pressing the + key right after.
This will not alter the given i, n, and PMT values.

Now, having figured this out, I thought to use the same method on the HP-12C.
The advice by Tony works as well here, but pressing the "+" key at the end is where this version differs.

I tried several times with both devices only to figure, that the HP-12C does work differently.

I investigated and I think, this comes down to where the given numbers and results are stored in each device.

The HP 12CP stores given financial values and the calculated result also in the stack.
e.g. if you give

0 -> PMT
1 -> n
19 -> i
238 -> FV
Press PV for net amount
= -200

If I look up the stack content after pressing PV on the HP-12CP with the R key, there is the following content
x = -200
Y = 238
Z = 38
T = 19

Press + for VAT amount = 38

If I look up the stack content on the HP-12CP with the R key now, there is the following content:
x = 38.00
Y = 19.00
Z = 1.00
T = 1.00

Now for the HP-12C:

If I look up the stack content after pressing PV on the HP-12C with the R key, there is the following content
x = -200
Y = 0.00
Z = 19.00
T = 19.00

Press + for VAT amount and the stack shows as follows:
x = -200.00
Y = 19.00
Z = 19.00
T = 19.00

This may be well known to the educated members and specialists on this board.

I just thought, this entry might add to the above mentioned thread by Kalevipoeg or the solution by Tony and avoid confusion for others.

Hope this helps someone and thank you Kalevipoeg and Tony for the provided help long time ago.

In case of any interest:

My HP-12CP was made in Phillippines, 2 batteries and on the front side, lower left, there is no "Hewlett . Packard" written, but plain the outer, continues line in silver. A sticker for serial #.

My pre-owned HP-12C was made in Malaysia, 3 batteries and has a stamped Serial #.

None of them has a securing screw on the battery lid.