Try these codes.

Previous page
Code:
$(substr,$(getvar,ctab),1,$(-,$(strlen,$(getvar,ctab)),2))$(substr,$(-,$(/,$(substr,$(getvar,ctab),$(-,$(strlen,$(getvar,ctab)),1)),100),0.009),3,2)
Next page
Code:
$(substr,$(getvar,ctab),1,$(-,$(strlen,$(getvar,ctab)),2))$(substr,$(+,$(/,$(substr,$(getvar,ctab),$(-,$(strlen,$(getvar,ctab)),1)),100),0.011),3,2)
These will work by taking the last two numbers and then either subtract 0.009 or add 0.011. The reason for the difference in the math is to require a character in the thousandths place. It then extracts the tenths and hundredths characters, and concatenates those two characters with the the layout name minus the last two characters.