The specific heat of twinned and detwinned single crystal samples of Y
Ba2Cu3O7-delta have been measured with magnetic fields up to 8 tesla a
pplied parallel to the c-axes of the crystals. The samples measured ha
d transition temperatures around 90 K and transition widths from 0.3 K
to 2 K. The data exhibits scaling behaviour characteristic of the 3-d
imensional-X-Y model with critical exponents consistent with those obs
erved in superfluid He-4. We then compare the scaling properties of th
e specific heat in the different samples and look for the 'universal'
nature of the scaling function.