Thanks Hartmut for the HP-15C test.
It seems HP-15C does *decimal* math, 10 significant digits, half-round-up
s = (a + b + c) / 2
= (1e5 + 99999.99979 + 0.00029) / 2
= (199999.9998 + 0.00029) / 2 -- round up
= 200000.0001 / 2 -- round up again
= 100000.0001 -- half-round-up
I have never seen a calculator like this ...
With this, I match your area result of 17.60681685 exactly.
On 2018年6月12日, Albert Chan wrote:
BTW, the article stated that heron formula return area = 17.6
I cannot reproduce it (even adjusting precision with gmpy2)
Anyone still have the old HP-15C calculator ?
yes :-) Keys still without bouncing, bright LCD, that's quality.
FWIW, my HP-15C tells 17.60681685 using the first formula in §1 on the
3rd example in Table 1, just tried. Else i have not followed the thread.
The 17.6 error comes from s: When it's 100000.000039999998989515
(Lua), Delta is 9.999999809638328685. But the HP-15C shows
s=100000.0001 , then it's 17.6068..., which you can confirm wit Lua.
Best Regards, Hartmut