[hp50g] how enter the rand function for graphing?

[ahahah]

hello
i want to trace the graph of this equation y1(x)= rand()
when i choose the "rand" function in menu math/prob it doesnt display "rand" but immediately it displays a random number (for example .25457641..)
so when i draw the y1 function it is a cunstant line and not a random value for each x

i don't know if i am clear..

my question: how to not have a value when i enter the rand function in y1(x) equation?
thx