tax calculation in purchase order

hi,

i have given BED@8,SED@5 and CST@10

overall tax rate is 23.

but when i entered the purchase order with quantity 100 and rate 10 my total amount is 1000

and tax is displaying as 243 rs ,

it seems my formulae is wrong , i have attached the screenshots.

can any one clarify me

bed formulae:

CENVAT_BED_BaseAmt=Total

CENVAT_BED_TaxAmt=CENVAT_BED_BaseAmt*CENVAT_BED_Rate

sed formulae

CENVAT_SED_BaseAmt=Total

CENVAT_SED_TaxAmt=CENVAT_SED_BaseAmt*CENVAT_SED_Rate

cst formulae

CST_BaseAmt=Total+CENVAT_BED_TaxAmt+CENVAT_SED_TaxAmt

CST_TaxAmt=CST_BaseAmt*CST_Rate

i have given common tax code as EX_CST( i have attached screen shot for this)

i have attached my purchase order for reference

thanks,

srinandha T