Hi @steveo4 Unfortunately it's trial and error, but as your on a pump you can set up a basal setting to cover the period whilst your working, if it were me and the work was strenuous then i'd set up a duplicate basal pattern on my pump and reduce basal profile by around 25%, and go from there and tweak up if doing a sedentary role, like anything it will require tweaking and it's never going to be perfect.
What is the work and what's happening to your levels ?