Calculating Alpha & Beta For Investment

hello again,

i wanted to know how i would calculate the alpha and beta of an investment, for example;

Beta Definition:

A measure of an investment's volatility, relative to an appropriate asset class. For stocks, the asset class is usually taken to be the S&P 500 index.

The formula is:

beta = [ Cov(r, Km) ] / [ StdDev(Km) ]2

where

r is the return rate of the investment;

Km is the return rate of the asset class.

Here is my example;

Return Invested
$34,000.00 $20,000.00 <---Money Invested
$24,000.00
-$2,300.00
-$5,000.00
----------
$50,700.00 <---- Total Return

The formula keys;

r = 253.50% Rate of return ($50,700.00/$20,000.00)

km = 10.00% Return Rate of Asset Class (Industry Average)

stdev = $19,318.97 Standard Deviation =stdev($34,000.00:-$5,000.00)

cov or covar <--- this is the one that stumps me, for covar, you need to columns of data, in my case, the returns of investment, since you need another table to compare data sets, what i did was, in the first column, it represents the amount of money invested each period, total money invested was $20,000.00/4 <--- total number of periods which = $5,000.00 as shown below;

Invested Return
$5,000.00 $34,000.00
$5,000.00 $24,000.00
$5,000.00 -$2,300.00
$5,000.00 -$5,000.00
---------- -----------
$20,000.00 $50,700.00

the formula for covar regarding the above table was =covar(a2:a5,b2:b5) but it equalled 0.000000000. What did i do incorrectly?

Second part, the alpha as defined means the measure of an investments
performance beyond what its beta would predict. How would you go about computing the alpha based on those tables? Once we know the beta through that formula mentioned above, how would you then calculate the alpha?

Look forward to hearing from you. Thank you for reading this...

Try this spreadsheet to calculate alpha and beta in Excel