How can I subtract excel cell values that contain both a number and alphabets

[Finian--]

I have measurement data from an ATE system where the results are given as both a number and 'unit' letters for example 22.3 dB, 2.109 MHz, 12.06 V and 0.175 A. To calculate temperature drift from these readings, I need to subtract cells that contain both a number and a letter i.e.2.012 MHz - 2.005 MHz = 0.007 does not matter if the answer contains the 'units' or not. Anyone know how I can achieve this ?

[QUENBY]

Assuming there is a space between the value and the suffix, you could strip the numeric value out of a cell this:
=LEFT(M30,FIND(" ",M30))
This will return all the characters in the string in M30 up to the space - this should be your numbers. You could then use this idea to subtract the numeric elements of two cells from each other thus:
=LEFT(M30,FIND(" ",M30))-LEFT(M31,FIND(" ",M31))
Hope this helps - unless there isn't a space between the number and the suffix, in which case I'll have to think again!

[Hollyn]

my last answer, just to be sure, you need to subtract 1 when you've found your space - thus, if the space occurs at the fourth position, you only want to see the first 3 characters, and so on. This version also adds the appropriate suffix onto the end of your formula.
=LEFT(M30,FIND(" ",M30)-1)-LEFT(M31,FIND(" ",M31)-1)&" Mhz"

[Finian--]

This was a GOOD problem. This final version strips the suffix from M30 and adds it, prefixed by a space, to your answer.
=LEFT(M30,FIND(" ",M30)-1)-LEFT(M31,FIND(" ",M31)-1)&"
"&RIGHT(M30,LEN(M30)-FIND(" ",M30))
I'll go away now.