How to calculate average voltage from a series of discrete points
Yes, since absolute value \$\Leftrightarrow\$ full wave rectification. For a perfect sine-wave, the MAV (Mean Absolute Value) is 0.637 of peak. In a general form:

$$E(MAV)=\frac{1}{T}\int_{0}^T|e(t)|dt$$

where \$e(t)\$ is the AC signal and \$T\$ is the time interval over which the average is the interest.

Measuring real waveforms, the precision of calculations depends on number of points taken. If measuring voltage, avoid the use of rectifier diodes - due to errors with voltage drops. Consider precision rectifiers based on op. amp. Another option (also with AD converter) is to handle the entire AC wave, with proper scaling and DC offset; and taking the absolute value in software.