How to calculate GPL from caustic soda solution

Take 10ml of the liquor solution and titrate it against 1N HCl/0.1N H2SO4 using phenolphthalein as an indicator. End Point will be pink to colorless.
Gpl= B.R x 4.

For % Strength Calculation:-
Weigh accurately   10ml of caustic and make up to a volume of 100ml with distilled water. Then from it take 10ml of solution and titrate it against 0.1N HCl/0.1NH2SO4 using phenolphthalein as an indicator. End Point will be pink to colorless.

%Strength = B.R x 4/wt.of solution. (B.Rx 0.1x0.04x10x100/wt.of sample)

Gpl for caustic on fabric.-
Take 100ml of distilled water on to the fabric and then boil it for 5 to 10mins and then titrate it against 0.1N HCl. By adding 3-4 drops of phenolphthalein (0.1%) solution. End Point will be pink to colorless.
1ml of 0.1N HCl=4mg NaOH 100%
g NaOH 100%/kg= B.R. of 0.1N HCl x 4/dry weight of the sample.