Serpentine/Snake ordering

I have a number of spreadsheets where I need to create a serpentine order. Each sheet has a column headed "Range" & next to it a column headed "Row". Each sheet has a different number of rows for each range. In the attached spreadsheet I need the Serp column for the "Early wheat" & TT canola to number 1-12, 24-13, 25-36, 48-37, 49-60, 72-61 but the GT canola has 8 rows so needs to number 1-8, 16-9, 17-24, 32-25, 33-40, 48-41.
The number of rows in each spreadsheet is at H1

Is there a formula to create this ordering?

Try this in A8:

=IF(ISODD(B8),COUNT($B$8:B8),B8*$H$1-COUNTIF($B$8:$B8,B8)+1)

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Welcome to the forum.

A bit cumbersome, but in A8 copied down:

=IF(ISTEXT(A7),1,IF(AND(AND(MOD(ROWS($1:1),$H$1)-1=0,ISEVEN(ROUNDUP(ROWS($1:1)/$H$1,0))),ISEVEN(ROUNDUP(ROWS($1:1)/$H$1,0))),ROUNDUP(ROWS($1:1)/$H$1,0)*$H$1,IF(ISEVEN(ROUNDUP(ROWS($1:1)/$H$1,0)),A7-1,IF(MOD(ROWS($1:1),$H$1)-1=0,($H$1*ROUNDUP(ROWS($1:1)/$H$1,0))-$H$1+1,A7+1))))

LOL! Go with the easy option!!!

For completeness, here's a way that needs no helper columns:

=IF(ISODD(ROUNDUP(ROWS($1:1)/$H$1,0)),ROWS($1:1),IF(MOD(ROWS($1:1),$H$1)-1=0,ROUNDUP(ROWS($1:1)/$H$1,0)*$H$1,A7-1))

No worries.

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I've just noticed you've updated your profile to Office 365, so we can further shorten it to this:

=LET(r,ROWS($1:1),rr,ROUNDUP(r/$H$1,0),IF(ISODD(rr),r,IF(MOD(r,$H$1)-1=0,rr*$H$1,A7-1)))

Just shout if you need any explanation.