如何限制textbox只入有關的數(編號：1772)

之前我用asciikey code 限制只可入".","1","2"....."0","k","G"
用val(text.text)取數 or text.text="XXXX"去check 入既數,但在textbox 內仍入兩個".","k"
怎樣才可限制只入這些數e.g.　".3","0.56","150k"---k=10既3次方,"190G"---G=10既6次方 ,而只能入一一個"k","G", "."