"P" is the luff length of the mainsail, measured along the aft face of the mast from the top of the boom to the highest point that the mainsail can be hoisted or black band.
"E" is the foot length of the mainsail, measured along the boom from the aft face of the mast to the outermost point on the boom to which the main can be pulled or to the black band.
"I" is measured along the front of mast from the genoa halyard to the main deck. The main deck is where the deck would be if there were no deckhouse.
"J" is the base of the foretriangle measured along the deck from the headstay pin to the front of the mast.
"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 from the highest spinnaker halyard to the deck.
"PY" and "EY" are, respectively the luff length and foot length of the mizzen of a yawl or ketch measured in the same way as for the mainsail.
"IY" is the measurement from the staysail halyard to the deck.
"JY" is the measurement from the staysail stay to the front face of the mast.
"LP" is the shortest distance between the clew and the luff of the genoa.