  Inflation produces nearly Harrison-Zel'dovich scalar and tensor perturbation
spectra which lead to anisotropy in the cosmic microwave background (CMB). The
amplitudes and shapes of these spectra can be parametrized by $Q_S^2$, $r\equiv
Q_T^2/Q_S^2$, $n_S$ and $n_T$ where $Q_S^2$ and $Q_T^2$ are the scalar and
tensor contributions to the square of the CMB quadrupole and $n_S$ and $n_T$
are the power-lawspectral indices. Even if we restrict ourselves to information
from angles greater than one third of a degree, three of these observables can
be measured with some precision. The combination $130^{1-n_S}Q_S^2$ can be
known to better than $\pm 0.3\%$. The scalar index $n_S$ can be determined to
better than $\pm 0.02$. The ratio $r$ can be known to about $\pm 0.1$ for $n_S
\simeq 1$ and slightly better for smaller $n_S$. The precision with which $n_T$
can be measured depends weakly on $n_S$ and strongly on $r$. For $n_S \simeq 1$
$n_T$ can be determined with a precision of about $\pm 0.056(1.5+r)/r$. A
full-sky experiment with a $20'$beam using technology available today, similar
to those being planned by several groups, can achieve the above precision. Good
angular resolution is more important than high signal-to-noise ratio; for a
given detector sensitivity and observing time a smaller beam provides
significantly more information than a larger beam. The uncertainties in $n_S$
and $r$ are roughly proportional to the beam size. We briefly discuss the
effects of uncertainty in the Hubble constant, baryon density, cosmological
constant and ionization history.
