Because it´s HIS one ... :)

You will have to test it! Just let Rybka play against Rybka, one using Sheebar.ctg and one using the new book by Harry Schnapp.
If I would know which one is stronger, i would say it on the download page.

>They are both defenited "very strong" books,so how can I know which one is stronger?

I will try to see this for very fast blitz time 1'+1'':

I'm running a 1+1 tournament with Rybka 1.1 having: Harry's book(95 MB), my book(3.42 GB) and Sheebar book(512 MB).
So it is Rybka 1.1 playing each other with 3 different books.

I will play 300-400 games for each engine i think.....
So far:

Rybka 1.1three    *********  36.0-28.0  30.5-33.5   66.5/128  52.0%
Rybka 1.1two      28.0-36.0  *********  38.0-26.0   66.0/128  51.6%
Rybka 1.1 32-bit  33.5-30.5  26.0-38.0  *********   59.5/128  46.5%

Rybka 1.1three uses your book, 1.1two my book and 1.1 32-bit Sheebar.

Harry's book is destroying mine while it loses to Sheebar, while my book is destoying Sheebar. Strange world! :)

Although it is losing, my book is full of traps and Harry's fall in two of them: :)

In Harry's book he has 3...e6 in the following game but it is on a grey colour and Chessbase GUI does not play it.
Yet the 3...dxe4 is playable but black should play in this line 8...Kc6! instead of 8...Kc7 Rybka played....
I will not reveal the other trap that the "HS_for_Rybka" book fall, sorry....

[Event "RRRbooks"]
[Site "Thessaloniki"]
[Date "2007.07.14"]
[Round "10.2"]
[White "Rybka 1.1two"]
[Black "Rybka 1.1three"]
[Result "1-0"]
[ECO "B21"]
[PlyCount "83"]
[EventDate "2007.07.14"]
[Source "Tsavdaris"]
[TimeControl "60+1"]

1. e4 {[%emt 0:00:00]} c5 {[%emt 0:00:00]} 2. f4 {[%emt 0:00:00]} d5 {
[%emt 0:00:00]} 3. Nf3 {[%emt 0:00:00]} dxe4 {
Black out of book. [%eval -24,11] [%emt 0:00:03]} 4. Ng5 {[%emt 0:00:00]} Nf6 {
[%eval -20,10] [%emt 0:00:04]} 5. Bc4 {[%emt 0:00:00]} Bg4 {
[%eval -46,11] [%emt 0:00:03]} 6. Qxg4 {[%emt 0:00:00]} Nxg4 {
[%eval -73,10] [%emt 0:00:01]} 7. Bxf7+ {[%emt 0:00:00]} Kd7 {
[%eval -98,5] [%emt 0:00:00]} 8. Be6+ {[%emt 0:00:00]} Kc7 {
[%eval -63,11] [%emt 0:00:04]} 9. Bxg4 {[%emt 0:00:00]} Qe8 {
[%eval -64,10] [%emt 0:00:02]} 10. Ne6+ {[%emt 0:00:00]} Kb6 {
[%eval -51,10] [%emt 0:00:02]} 11. Na3 {[%emt 0:00:00]} a6 {
[%eval -48,10] [%emt 0:00:02]} 12. d3 {[%emt 0:00:00]} Ka7 {
[%eval -61,9] [%emt 0:00:02]} 13. Be3 {[%emt 0:00:00]} Qg6 {
[%eval -66,11] [%emt 0:00:05]} 14. Bh3 {[%emt 0:00:00]} exd3 {
[%eval -41,10] [%emt 0:00:01]} 15. O-O-O {[%emt 0:00:00]} b6 {
[%eval -11,11] [%emt 0:00:06]} 16. Rxd3 {[%emt 0:00:00]} Qe4 {
[%eval 0,11] [%emt 0:00:02]} 17. Re1 {
White's last book move. A winning position. [%emt 0:00:00]} Qc6 {
[%eval 29,11] [%emt 0:00:04]} 18. Nc4 {(Re1-d1) [%eval 112,10] [%emt 0:00:03]}
Nd7 {[%eval 118,10] [%emt 0:00:04]} 19. Red1 {[%eval 176,11] [%emt 0:00:02]}
Nf6 {[%eval 172,11] [%emt 0:00:02]} 20. Nxb6 {[%eval 178,12] [%emt 0:00:05]}
Qxb6 {[%eval 186,11] [%emt 0:00:02]} 21. Bxc5 {[%eval 207,11] [%emt 0:00:02]}
Qxc5 {[%eval 225,13] [%emt 0:00:02]} 22. Nxc5 {[%eval 234,12] [%emt 0:00:02]}
e5 {[%eval 241,12] [%emt 0:00:02]} 23. Nd7 {[%eval 245,12] [%emt 0:00:03]} exf4
{[%eval 245,11] [%emt 0:00:01]} 24. Nxf6 {[%eval 253,11] [%emt 0:00:01]} gxf6 {
[%eval 256,11] [%emt 0:00:02]} 25. Rb3 {(Rd3-d7+) [%eval 268,11] [%emt 0:00:02]
} Rb8 {[%eval 264,12] [%emt 0:00:01]} 26. Rd7+ {[%eval 267,11] [%emt 0:00:01]}
Ka8 {[%eval 257,12] [%emt 0:00:01]} 27. Bf5 {[%eval 261,12] [%emt 0:00:04]}
Rxb3 {[%eval 261,12] [%emt 0:00:02]} 28. cxb3 {[%eval 268,12] [%emt 0:00:03]}
h6 {(Ka8-b8) [%eval 265,10] [%emt 0:00:01]} 29. Be4+ {
(Rd7-f7) [%eval 258,10] [%emt 0:00:02]} Kb8 {[%eval 264,5] [%emt 0:00:00]} 30.
b4 {(Rd7-b7+) [%eval 266,12] [%emt 0:00:03]} Kc8 {
(h6-h5) [%eval 269,12] [%emt 0:00:02]} 31. Ra7 {[%eval 266,12] [%emt 0:00:03]}
Bd6 {[%eval 276,12] [%emt 0:00:03]} 32. Ra8+ {[%eval 277,11] [%emt 0:00:02]}
Bb8 {[%eval 275,11] [%emt 0:00:00]} 33. Rxa6 {[%eval 281,12] [%emt 0:00:02]}
Be5 {(Rh8-f8) [%eval 280,11] [%emt 0:00:02]} 34. Ra8+ {
[%eval 288,11] [%emt 0:00:02]} Bb8 {[%eval 288,11] [%emt 0:00:00]} 35. Kc2 {
(b4-b5) [%eval 288,12] [%emt 0:00:04]} Re8 {
(Kc8-d7) [%eval 295,10] [%emt 0:00:01]} 36. Bf3 {[%eval 325,12] [%emt 0:00:03]}
Re1 {(Re8-d8) [%eval 323,11] [%emt 0:00:02]} 37. a4 {
(b4-b5) [%eval 360,12] [%emt 0:00:02]} Rf1 {
(Re1-e7) [%eval 350,11] [%emt 0:00:04]} 38. a5 {
(b4-b5) [%eval 404,14] [%emt 0:00:02]} Rxf3 {
(Rf1-f2+) [%eval 404,14] [%emt 0:00:02]} 39. gxf3 {
[%eval 1023,16] [%emt 0:00:04]} Kb7 {[%eval 1116,17] [%emt 0:00:04]} 40. Rxb8+
{[%eval 1749,17] [%emt 0:00:09]} Kxb8 {[%eval 1039,15] [%emt 0:00:01]} 41. b5 {
(Kc2-d3) [%eval 2160,17] [%emt 0:00:01]} Kc8 {
(Kb8-c7) [%eval 971,14] [%emt 0:00:01]} 42. Kd3 {[%eval 2885,16] [%emt 0:00:03]
} 1-0

My impression so far is that Harry's book is very deep although "only" 95 MB in comparison with Sheebar which is 512 MB and mine which is 3.42 GB.
I've compared some lines and my book is much deeper, but it seems Harry found a way to put lines that Rybka likes very much. I have seen this in 3 games until now. Although Sheebar and my book created a position which is better for one color, Rybka played badly with that color and lost.
So Harry's books seems indeed an optimized for Rybka book....

As for the depth which is very deep in Harry's book and in 2 cases even "out-booked" mine and Sheebar, i wondered how is it possible with such a small book in comparison with my 3.42 GB and Sheebar's 512 MB. I think that the answer is that my book for example(i don't know about Sheebar) has millions of risky lines that contain all the different variations up to the endgame while Harry's book is more solid with only "logical" moves. Ideal for Rybka i would say.... :)