As stated in the provably fair details:
Two strings are created :
STRING1 = "[NONCE]:[SERVER SEED]:[NONCE]"
STRING2 = "[NONCE]:[CLIENT SEED]:[NONCE]"
For your last roll :
STRING1 = "194473:92dadcac8a291aad1265ea20c36dfb1e39a5f8ff76de414a51f13abcd9388e98:194473"
STRING2 = "194473:3mTVs5wr2Qa1wVZt:194473"
Then HMAC-SHA512 is used to hash STRING1 with STRING2 as the secret key, giving us a 128 character hex string.
The first 8 characters of the hex string are taken and converted to a decimal.
This decimal is then divided by 429496.7295 and rounded off to the nearest whole number.
This whole number is used as your roll, with the maximum possible value being 10,000.
I'm not sure what you mean by "halfway between two others". 1.4999999 is nearest 1 and 1.5000000 is nearest 2 so there can't be a number halfway.