Third, here is the (long) walkthrough:

Let me start by explaining how I am going to refer to each cell. I will name each 3x3 grid with a capital letter, starting in the top left corner and going to the right. So they are:

ABC

DEF

GHIJK

LMN

OPQ

And in each grid I will name each cell with a lower case letter, again starting in the top left and going to the right. So they are:

abc

def

ghi

So the top most row would consist of cells Aa, Ab, Ac, Ba, Bb, Bc, Ca, Cb, and Cc.

And we begin...

Grids D, G and H:

· 360 = 5*(72) so either Gb, Ge or Gf is 5.

· 15 = 5*(3). Ga can't be 5 due to the 5 in either Gb, Ge or Gf. So **Dg=5** and **Ga=3**.

· 70 = 5*(14). Di can't be 5 due to the 5 in Dg. Gc can't be 5 due to the 5 in either Gb, Ge or Gf. So **Ha=5**.

· 42 = 7*(6) so either Gd or Gg is 7.

· 70 = 7*(10). Gc can't be 7 due to the 7 in either Gd or Gg. So **Di=7** and **Gc=2**.

· 4 = 1+3. Gi can't be 3 due to the 3 in Ga. So **Hg=3** and **Gi=1**.

· 42 = 6*7 (Gd and Gg), and 360 = 5*8*9 (Gb, Ge and Gf). So for grid G to have a 4 it must be that **Gh=4**.

Grids A, B and C:

· 127 = 7*(18). Aa and Ad can't be 7 due to the 7 in either Gd or Gg. So **Ab=7**.

· 224 = 7*(32). Ai and Dc can't be 7 due to the 7 in Di. So **Bg=7**.

· 15 = 5*(3). We need a third factor so we must have 15 = 5*3*1. Ba can't be 5 due to the 5 in Ha, and it can't be 3 due to the 3 in Hg. So **Ba=1**.

· 56 = 7*(8). Cc can't be 7 due to the 7 in Ab. So **Cf=7** and **Cc=8**.

Grids L, M, O and P:

· 378 = 7*(54) so either Ob, Oe or Of is 7.

· 21 = 7*(3). Oa can't be 7 due to the 7 in either Ob, Oe or Of. So **Lg=7** and **Oa=3**.

· 5 = 5/1 is the only way to have this division with digits <= 9. So Md and Mg are 1 and 5.

· 6 = 1+5 = 2+4. Pg can't be 1 or 5 due to the 1 and 5 in Md and Mg. So Oi and Pg are 2 and 4.

· 8 = 8/2 = 4/1 are the only ways to have this division with digits <= 9. Either way, Od and Og can't be 5.

· 378 = 7*6*9 (Ob, Oe and Of), and 288 = 8*6*6 = 8*4*9 (Oc). So for grid O to have a 5 it must be that **Oh=5**.

· 378 = 7*6*9 (Ob, Oe and Of), 288 = 8*6*6 = 8*4*9 (Oc), and 6 = 2+4 (Oi). So for grid O to have a 1 it must be that Od or Og is 1, which means Od and Og are 1 and 4. Og can't be 4 since either Oi or Pg is 4. So **Od=4** and **Og=1**.

· 6 = 2+4. Oi can't be 4 due to the 4 in Od. So **Pg=4** and **Oi=2**.

· 378 = 7*6*9 (Ob, Oe and Of). So for grid O to have an 8 it must be that **Oc=8**.

Grids J, K and N:

· 180 = 5*(36) so either Kd, Ke or Kh is 5.

· 40 = 5*(8). Ka can't be 5 due to the 5 in either Kd, Ke or Kh. So **Jc=5** abd **Ka=8**.

· 243 = 3^5. The only way this can be arranged into three factors <= 9 is if we have 243 = 9*9*3. We can't have two 9s in the same row or column so we must have **Kg=3**, **Ji=9** and **Na=9**.

· 180 = 5*(36) = 5*6*6 = 5*4*9. We can't have two 6s in the same grid so we must have 180 = 5*4*9. Kd and Kh can't be 9 due to the 9s in Ji and Na. So **Ke=9**.

Grids P and Q:

· 360 = 5*(72) = 5*8*9. Qh and Qi can't be 5 due to the 5 in Oh. So **Qf=5**. Qh can't be 9 due to the 9 in Ke. So **Qi=9** and **Qh=8**.

· The 5 in grid P can't be in the left column due to the 5 in either Md or Mg. 5 can't be in the right column due to the 5 in Jc. 5 can't be in the middle or bottom row due to the 5s in Qf and Oh. So **Pb=5**.

Grids I, M and Q (long diagonal):<o:p></o:p>

· Qa, Qe and Qi can't be 5 due to the 5 in Qf.

· Ma, Me and Mi can't be 5 due to the 5 in either Md or Md.

· Ia cant' be 5 due to the 5 in Ha (and Jc). Ie can't be 5 due to the 5 in Oh. So **Ii=5**.

Grid K:

· 180 = 5*4*9. Kh can't be 5 due to the 5 in Ii. So **Kd=5** and **Kh=4**.

Grids K, M and O (long / diagonal):

· Kc, Ke and Kg can't be 5 due to the 5 in Kd.

· Oc, Oe and Og can't be 5 due to the 5 in Oh.

· Mc can't be 5 due to the 5 in Jc. Me can't be 5 due to the 5 in Pb. So **Mg=5** and **Md=1**.

Grids I, L, O and P:

· The 7 in grid I can't be in the left or right columns due to the 7s in Lg and Cf. So Ib, Id or Ih is 7.

· 378 = 7*6*9. Ob and Oe can't be 7 due to the 7 in Ib, Id or Ih. So **Of=7**. Oe can't be 9 due to the 9 in Ke (diagonal rule). So **Ob=9 **and **Oe=6**.

· 288 = 8*6*6 = 8*4*9. Pa can't be 4 or 9 due to the 4 in Pg and the 9 in Ob. So we must have 288 = 8*6*6. So **Pa=6** and **Li=6**.

Grid Q:

· 6 can't be in the top or middle rows due to the 6s in Pa and Oe. So **Qg=9**.

· 3 can't be in the top row due to the 3 in Oa and 3 can't be in the left column due to the 3 in Kg. So **Qe=3**.

Grid M:

· 9 can't be in the diagonal due to the 9 in Qi. 9 can't be in the top row due to the 9 in Na. And 9 can't be in the right column due to the 9 in Ji. So **Mh=9**.

Grid I:

· 9 can't be in the diagonal due to the 9 in Qi. 9 can't be in the middle or bottom rows due to the 9s in Ke and Ji. 9 can't be in the middle column due to the 9 in Ob. So **Ic=9**.

Grid L:

· 9 can't be in the middle or right columns due to the 9s in Ob and Ic. 9 can't be in the top row due to the 9 in Na. So **Ld=9**.

· 5 can't be in the middle or right columns due to the 5s in Oh and Ii. So **La=5**.

· 14 = 5+(9). Since grid L already has 9, 7, 6, and 5 placed, the only way to have two digits add up to 9 is if they are 1 and 8. Lc can't be 8 due to the 8 in Oc. So **Lb=8** and **Lc=1**.

Grids A, E and I (long diagonal):

· Aa, Ae and Ai can't be 7 due to the 7 in Ab.

· In grid J, 56 = 7*(8) so either Jd, Je or Jf is 7.

· Ia, Ie and Ii can't be 7 due to the 7s in Lg, Of and either Jd, Je or Jf.

· Ea can't be 7 due to the 7 in Bg. Ei can't be 7 due to the 7 in Di. So **Ee=7**.

Grid G:

· 360 = 5*8*9. Gb can't be 5 or 9 due to the 5 in Ha and the 9 in Ic. So **Gb=8**.

· 42 = 7*6. Gg can't be 7 due to the 7 in Ee (diagonal rule). So **Gd=7** and **Gg=6**.

Grid E:

· 24 = (2^3)*3 = 8*3 = 4*6. Ed and Eg can't be 3 due to the 3 in Hg. So it must be that 24 = 4*6. Eg can't be 6 due to the 3 in Gg (diagonal rule). So **Ed=6** and **Eg=4**.

Grid I:

· The top and bottom row can't have a 3 due to the 3s in Ga and Hg. The left column can't have a 3 due to the 3 in Oa. 3 can't be in the diagonal due to the 3 in Qe. So **If=3**.

· Consider the column that starts at Ia and ends at Og. Ia can only be 2, 6 or 8 due to the numbers placed in this column so far. Ia can't be 2 or 8 due to the 2 in Gc and the 8 in Gb. So **Ia=6**.

Grid J:

· 56 = 7*8 = 7*8*1 = 8*4*2. Either way, Jd, Jd and Jf can't be 6.

· The top row can't have a 6 due to the 6 in Ia. The left column can't have a 6 due to the 6 in Pa. So **Jh=6**.

Grid K:

· The top and bottom rows can't have a 6 due to the 6s in Ia and Jh. So **Kf=6**.

Grid M:

· 6 can't be in either or / diagonal due to the 6s in Ia and Oe. The middle column can't have a 6 due to the 6 in Jh. So **Mf=6**.

· The top row can't have an 8 due to the 8 in Lb. 8 can't be in the / diagonal due to the 8 in Oc. So **Mi=8**.

· 3 can't be in either or / diagonal due to the 3s in Qe and Kg. So **Mb=3**.

Grid N:

· The left and right columns can't have a 6 due to the 6s in Qg and Kf. The middle and bottom rows can't have a 6 due to the 6s in Mf and Li. So **Nb=6**.

· The left and right columns can't have a 5 due to the 5s in Kd and Qf. The bottom row can't have a 5 due to the 5 in Mg. So **Ne=5**.

· The top and bottom rows can't have an 8 due to the 8s in Lb and Mi. The left column can't have an 8 due to the 8 in Ka. So **Nf=8**.

· The left and middle columns can't have a 3 due to the 3s in Kg and Qe. The top row can't have a 3 due to the 3 in Mb. So **Ni=3**.

Grid P:

· The top and middle rows can't have a 3 due to the 3s in Oa and Qe. The middle column can't have a 3 due to the 3 in Mb. So **Pi=3** (how fitting!).

· Consider the row that starts at Og and ends at Qi. Ph can only be 7 due to the numbers already placed in this row so far. So **Ph=7**.

· The middle and right columns can't have a 9 due to the 9s in Mh and Ji. So **Pd=9**.

· The right column can't have an 8 due to the 8 in Mi. So **Pe=8**.

Grid L:

· The bottom row can't have 3 due to the 3 in Ni. The right column can't have a 3 due to the 3 in If. So **Le=3**.

· The right column can't have a 2 due to the 2 in Oi. So **Lh=2**.

· The only remaining number is 4 so **Lf=4**.

Grid M:

· The left column can't have a 4 due to the 4 in Pg. The middle row can't have a 4 due to the 4 in Lf. So **Mc=4**.

· The middle column can't have a 7 due to the 7 in Ph. So **Ma=7**.

· The only remaining number is 2 so **Me=2**.

Grid N:

· The top and bottom rows can't have a 7 due to the 7s in Ma and Lg. So **Nd=7**.

· The bottom row can't have a 2 due to the 2 in Lh. So **Nc=2**.

· The middle column can't have a 4 due to the 4 in Kh. So **Ng=4**.

· The only remaining number is 1 so **Nh=1**.

Grid K:<o:p></o:p>

· The right column can’t have a 2 due to the 2 in Nc. So **Kb=2**.<o:p></o:p>

· The / diagonal can’t have a 1 due to the 1 in Og. So **Ki=1**.<o:p></o:p>

· The only remaining number is 7 so **Kc=7**.<o:p></o:p>

<o:p></o:p>

Grid Q:<o:p></o:p>

· The left and right columns can’t have a 7 due to the 7s in Nd and Kc. So **Qb=7**.<o:p></o:p>

· The left column can’t have a 4 due to the 4 in Ng. So **Qc=4**.<o:p></o:p>

· The \ diagonal can’t have a 2 due to the 2 in Me. So **Qd=2**.<o:p></o:p>

· The only remaining number is 1 so **Qa=1**.<o:p></o:p>

<o:p></o:p>

Grid P:<o:p></o:p>

· The top row can’t have a 1 due to the 1 in Qa.