The Mid function will work fine, as long as the pressure value is in the same relative position in the text string.
The following macro will extract the pressure value regardless of the position in the string.
It assumes your pressure readings will be greater than 99 and less than 1,000. It further assumes that the text string is in cell A1 and you wish to return the pressure in cell B1. Modify the cell references as needed.
Copy the following macro to the clipboard:
For i = 1 To Len(Range("A1"))
If IsNumeric(Mid(Range("A1"), i, 1)) And _
IsNumeric(Mid(Range("A1"), i + 1, 1)) And _
IsNumeric(Mid(Range("A1"), i + 2, 1)) Then
Range("B1").Value = Mid(Range("A1"), i, 3)
Press ALT + F11
In the menus at the top of the VBE, select INSERT > MODULE
Paste the macro into the module editing area to the right.
Close the VBE and return to the worksheet.
Press ALT + F8
When the Macros window opens, highlight the macro and click 'Options..'
Enter a letter to be used as a keyboard shortcut and click 'OK'.
Press CTRL + your shortcut letter to run the macro.
Alternatively, in addition to calling the macro with a keyboard shortcut, you could call the macro in the Workbook_Open event and have the value automatically extracted.
Copy the following code to the clipboard:
Private Sub Workbook_Open()
Press ALT + F11
Double click 'THIS WORKBOOK' in the Microsoft Excel Objects in the upper left quadrant.
Paste the code into the workbook module editing area to the right.
Close the VBE and save the workbook.
Note: If the pressure value could be <100 or >999, the macro could be modified to accommodate those values.