I'm practising scientific notation on my calculator. Unfortunately, it's a no-name scientific calculator so I can't any manual online.

I tried to do the following:
4.007 [EXP] 7 [+/-] [=]
It gives me 0.0000004 instead of 0.0000004007

I assume its memory is limited. Then I tried it on my computer scientific calculator (kcalc on linux). I enabled the maximum number of digits to 30. I did the following:

4.007 [X*10y] 7 [+/-]
and I'm left with 4.007e-7 on the display. When I press [=] it changes to 4.007e-07 and nothing else. I tried it with some other lower (negative) exponents and it worked fine. What can be the reason?

Can you recommend any scientific calculators?

thanks in advance