Financial HP Calculator: Amortisation with Payments at begin of period

[Gil]

Take PV=10000
FV = 0
I%Y = nominal 12
P/Y = 12 (or 1)
Total of Payments 60 (or 5 if P/Y=1)
Mode of Payments =Begin
Then Solve for corresponding Payments

B1) Go to Armotize Plan
Choose 60 (or 5 if P/Y=1) for Payments
Press Armotize —> Balance ± 0

B2) Repeat A)
with same initial data, PV = 10000
Go to Armotize Plan
Choose 30 (or 1 if P/Y=1 and total N=5) for Payments
Press Amortize
Repeat the process once for the remaining 30 Payments
—> Final Balance ≠ zero on my HP50G (final balance = -75.8524360235)
(Or, if P/Y=1 and total N=5), repeat the process 4 times with each time only 1 Payment to be amortized:
Interests on my HP50G are given as 5 times = 0, but 0 should be always valid once, ie only for the very first (amortisation) Payment during the whole amortisation process. With P/Y=1 and total N=5, amortizing 5 times, each time with 1 Payment, gives an unwished final balance of -2384.3630331).

Could somebody owning a financial calculator (HP, TI, CASIO, etc.) check that "logical" (payments at beginning, —> interest each time for a period = 0 —> interest = 0) but confusing" issue, that does not correspond to the wished result?

Many thanks in advance for your painstaking.

I understand now, in that special case of PMT at begin, that, after launching the first time the amortisation with the initial chosen number of Payments (in my case, 30) and pressing B—>PV, we are back at the normal situation "Payments at the End".
Therefore, to get the expected/wished next amortisation results with the HP50G, we have simply to return to main, initial menu (the one that solved for PMT) and modify the settings: a) change N=60 into N-"previous already amortised payments", ie N-30 = 60-30 =30, and b) let here, now, option END payment (instead of BEGIN) and then only carry on normally with the usual amortisation.

Not very complicate, indeed, but needs attention/reasoning, and consequent manipulations/changes (back once in the previous PMT Solver menu and back to amortisation menu).

Regards,
Gil