VB编程请教

这个程序怎么编：
text1中输入数值a1。点击command2，在text2中输出结果。要求：当a1<=375时，a2=0.571.当a1<=425时，a2=0.525.当a1<=475时，a2=0.491.当a1<=525时，a2=0.457.当a1<=575时，a2=0.431.当a1<=625时，a2=0.405.当a1<=675时，a2=0.384.当a1<=725时，a2=0.363.当a1<=775时，a2=0.3466.当a1<=850时，a2=0.33.当a1<=950时，a2=0.31. 当a1=其他的时候，输出“输入有误，请重新输出”

各位高手帮帮忙啊~~~~感激不尽

Private Sub Command2_Click()
On Error GoTo errline
Dim a1 As Long
Dim a2 As Double

a1 = Text1.Text
Select Case a1

Case Is <= 375
a2 = 0.571
Case Is <= 425
a2 = 0.525
Case Is <= 475
a2 = 0.491
Case Is <= 525
a2 = 0.457
Case Is <= 575
a2 = 0.431
Case Is <= 625
a2 = 0.405
Case Is <= 675
a2 = 0.384
Case Is <= 725
a2 = 0.363
Case Is <= 775
a2 = 0.3466
Case Is <= 850
a2 = 0.33
Case Is <= 950
a2 = 0.31
Case Else
MsgBox "输入有误，请重新输出"
Exit Sub
End Select
MsgBox a2
Exit Sub
errline: