Standard Deviation Map Formula:

sqr((([Average Yield]-[Yield_2002s 3])*([Average Yield]-[Yield_2002s 3])+([Average Yield]-[Yield_2003c 3])*([Average Yield]-[Yield_2003c 3])+([Average Yield]-[Yield_2004s 3])*([Average Yield]-[Yield_2004s 3])+([Average Yield]-[Yield_2005c 3])*([Average Yield]-[Yield_2005c 3])+([Average Yield]-[Yield_2006s 3])*([Average Yield]-[Yield_2006s 3]))/4)

Yield Classes Formula:

IIf([Average Yield]>1+[StDev Yield],1,IIf([Average Yield]<1-[StDev Yield],-1,0))