Calculate N using the provided data and formula: N = [40 sqrt(n sum(x2) - (sum(x))2) / sum(x)]2

The number of individual readings, $n$, is the count of the values in the 'reading $0.01 \text{min (x)}$' row.

$$n = 7$$

The summation of individual readings, $\sum x$, is given in the 'Total' column for the 'reading $0.01 \text{min (x)}$' row.

$$\sum x = 41$$

The summation of squares of each reading, $\sum x^2$, is given in the 'Total' column for the '$x^2$' row.

$$\sum x^2 = 247$$

The formula is:

$$N = \left[ \frac{40 \sqrt{n \sum x^2 - (\sum x)^2}}{\sum x} \right]^2$$

Substitute the values:

$$N = \left[ \frac{40 \sqrt{7 \times 247 - (41)^2}}{41} \right]^2$$

First, calculate $n \sum x^2$:

$$7 \times 247 = 1729$$

Next, calculate $(\sum x)^2$:

$$(41)^2 = 1681$$

Now, subtract these values:

$$1729 - 1681 = 48$$

$$N = \left[ \frac{40 \times 6.928203}{41} \right]^2$$ $$N = \left[ \frac{277.12812}{41} \right]^2$$ $$N = \left[ 6.759222 \right]^2$$

$$N \approx 46$$

The required number of observations is $\text{46}$.