Integration on WP 34S

[lrdheat]

Impressed at how well integration is handled on the WP 34S on my DM 42 platform. I was surprised to see that e^-x from 0 to infinity (yes, the WP 34S has the ability to enter infinity!) came out as 1. Most of my calculators will show “1” for an integration range from 0 to 1000, but will miss the important part of the function if integrated from, say, 0 to 10000, and report “0” (Prime in home does report “1” for large numbers). The HP 42S does see the important part of the function using 0 to 10,000 and does report 1.

Question: While the WP 34S does correctly “see” the important part of the function when using 0 to infinity, it, like most of my other calculators, shows “0” if I use an interval of 0 to 40000. Why does it work when using infinity, but fail for large specific numbers?