How do I use a sub VI to read/write to objects on the calling VI's front panel?

[Dave123]

Hi,
I'm trying to break a LabView program down into sub VI's called by the
main VI and for example want to create a sub VI that will initialise
the value of indicators and controls on the front panel of my main VI.
I've tried creating a global VI with these in and refering to them in
my sub vi. It runs without any errors but they do not get updated in
the main VI after the sub vi has changed them. Is this the right way
to do this and if so why won't it work?

Thanks,
Dave G