I = Height of headstay termination above the sheer line.
J = Distance between the headstay termination at the deck and the front of the mast at the sheer line.
P = Distance between black bands on the mast, or the maximum luff length of the main.
E = Distance between black bands on the boom, or the maximum foot length of the main.
JSP is the length of the spinnaker pole or the distance from the forward end of the bowsprit (fully extended) to the front face of the mast.
ISP is measured form the highest spinnaker halyard to the deck.
PY & EY are similar to P & E, but indicate mizzen dimensions.