Hi Robin,

One problem is that the UDF is in a different addin so I cannot run a public
variable and use this as a get out clause when the UDF triggers.

If there's nothing you can do modify the UDF source, one option is to wrap
your own UDF around it, within which you can respond to have a public 'DoCalc'
boolean.

Regards

Stephen Bullen
Microsoft MVP - Excel
www.BMSLtd.co.uk