"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.
"E" is the foot length of the main-sail, measured along the boom from the after face of the mast to the outermost point on the boom to which the main can be pulled.
"I" is measured along the front of mast from the highest halyard to the main deck. The main deck is where the deck would be if there were no coach roof.
"J" is the base of the foretriangle measured along the deck from the head stay to the mast.
"TPS" is the length along the deck from the front of the mast to the forward end of the sprit in the fully extended position.
"PY" and "EY" (Not Shown In Diagram) are, respectively the luff length and foot length of the mizzen of a yawl or ketch measured in the same manner as for the mainsail.
"IY" is the "I" measurement for the staysail halyard.
"JY" is the base of the staysail foretriangle measured along the deck from the staysail stay to the mast.