Slope formula for only last two rows when adding row

[dbcooper88]

Going to add rows daily. I just want the slope for last two days. Looking for slope formula for only last two rows after I add a row/line at the bottom. For example my x is A1:A2 and my y is B1:B2. Adding row with coordinates are A3 and B3. Whats the slope formula for just the last two rows/lines ? TIA

 

[Ken Cowen]

If you don't have anything else in columns A or B, the following should do it

=(OFFSET(B1,COUNTA(B:B)-1,0)-OFFSET(B1,COUNTA(B:B)-2,0))/(OFFSET(A1,COUNTA(A:A)-1,0)-OFFSET(A1,COUNTA(A:A)-2,0))

This can be anywhere outside of columns A or B.

I hope this helps.

Ken