that was awesome! that is exactley what i needed thank you so much.
now, is it possible for me to modify what you gave me to something like this
IIf([Forms]![FrmParam]![chkboxThermPS],[Forms]![FrmParam]![TxtBoxmintps]<=[Thermal Power Steady, kW#]<=[Forms]![FrmParam]![TxtBoxmaxtps],True)...