In determining viscosity (eta) by poiseuille.s method the formula used eta = (pi p r^4)/( 8 v1). Which of the quantities in the formula must be measured more accurately

In determining viscosity (eta) by poiseuille.s method the formula used

1.	In determining viscosity (eta) by poiseuille.s method the formula used eta = (pi p r^4)/( 8 v1). Which of the quantities in the formula must be measured more accurately
Answer» <P>`p` `R` `V` `1` ANSWER :B