Question on Chapter 8 Challenge second paragraph.

So, a short 2-byte (16 bit) integer, and one bit is used to hold the sign (+ or -).

The way to find the values for these are a bit unclear for me. On page 42 a uS 8-bit number is calculated by 2^8 = 256. Because 2^8 bits. THen you minus one for the +/- sign or because you are starting at 0?

Then it goes on to say a signed 64 bit number is calculated by 2^63. Right there I am confused, why are you not doing the calculation of 2^64. Then minus one bit for the sign?

If someone could give me a comparison and details/explanations for the unsigned and signed 8 bit numbers.

How do you calculate the signed 8-bit and what is range? How do you calculate unsigned 8-bit and what is range?

Thanks