Download the YASAI.XLA file and store on your disk. Do not open it direclty in Excel
Start Excel
Select Tools->Add-ins
Select Browse
Find YASAI.XLA and click OK.
If it asks you whether to copy a file, say yes
If your version of Excel is not English, you might get an error here. It is not fatal. Say "stop".
"Yasai Simulation..." should now be on the Tools Menu
If "Yasai Simulation..." is not on the Tools menu, you can still run a simulation as follows:
Select Tools->Macro->Visual Basic Editor
Find YASAI_Param->Forms->FrmSimMenu on the top left pane
Click the "Play" (►) button on the top bar