Definitely not the HP 80 or 81, as they don't have an IRR function.

At this point I couldn't even recommend them for TVM calculations, as they don't have dedicated TVM registers, but instead depends on the user entering the information in the correct order. In other words, if you press the sequence "3 N 4 i 5 PV", you end up with the 3, 4, and 5 on the stack. The order in which you use the TVM keys just tells it which TVM calculation (out of a limited set) you're trying to compute. And if you do calculations on the stack in the process, you can push your TVM values out.

The HP-70, HP-22, and HP-27 have dedicated TVM registers, but do not use the modern five-variable TVM with signed cash flow direction.

The modern TVM was first introduced in the HP-92 (desktop printing),

and used in the 37E, 38E/C, 12C, and all of the newer (Saturn and post-Saturn) models.

Hi, Glen;

just to add my contribution after Eric's post.

Considering the keystroke sequences you need, the HP17B is the one you must press more keys to get to the IRR. I actually own an HP17BII, an HP17BII+ and an HP19BII, and all of them need essentially the same keystroke sequence to compute IRR. I also have an HP10BII and an HP14B, and in these two, you can compute IRR with less keystrokes Of course, we must remember that they have limited memory to cash flow entries when compared to the first ones.

Accuracy and speed must be checked in each case. The new ones are faster, the HP10B is probably the slowest amongst the ones mentioned above. The HP10BII, although not an HP-original design, is surprinsingly fast. No comments about quality, though...

My 2ยข.

Cheers.

Luiz (Brazil)

Actually the HP-81 does have an IRR function. There's no key on the keyboard for it, you use the EXT() key followed by a '1' after entering up to 9 cash flows in registers 1-9. The initial amount goes into PV and the number of flows in N.

The 81 is much more than a desktop, printing version of the 80. It's got 20 registers and a bunch more functions than appear on the keyboard.

hey Luiz, I WILL comment about the hp10B11 quality. Save yourself the pain and get a 10B off e-bay. My 10B11 died in less than 2 years. At least it wasn't a slow death.

I use the 10B for irr and get along o.k. However, I am an ordinary head of household guy, not a master of the universe money guy, so your needs may be more sophisticated.

Having bought dozens of 10B's for myself and acquaintances, the vintage I prefer is the 1996. Quality suffers somewhat after 1996.

don