acceleration output interpretation
Maybe it would help to read the part of the datasheet where it tells you the output units?

From page 12 of the datasheet:
Linear acceleration sensitivity FS = ±16g  0.732mg/LSB

So take the reading, multiply by 0.732 and then divide by 1,000 to get the acceleration in g.

1340 * 0.732 / 1000 = 0.981g

edit - Note that is 0.981g NOT 9.81m/s, it's 20mg off, well within the margin of error of the sensor, that the value happens to be the same digits as 1g measured in m/s is just a confusing coincidence.