A Y-VAR represents a one independent variable mathematical function. The independent depends on the mode the Y-Var is associated with. Func mode Y[0-9] use X, Polar Y-Vars r[1-6] use θ, Param mode T[X,Y][1-6] use T and Seq mode u,v and w use n.
Y-VARs are stored as strings, but return a Real. For example
"1+1"→Y1 is a legal statement,
Y1→A is a legal statement, be neither
Y1→Str1 is allowed.
Additionally to just using the variable, one can use a construction like
Y1(4) to get the value of the expression when the independent variable for that mode is the value in parenthesis.