What are the systematic errors in measuring the speed of sound in air?

[roam]

Homework Statement

I want to carry out an experiment in order to make accurate measurement of the speed of sound in air.

Method:
We will measure the speed of sound waves in air by measuring the time required for a short sound pulse to travel from its source to a receiver. This time interval is short and is
measured with the help of an instrument called an oscilloscope. The experimental setup is shown in the figure below:

[PLAIN]http://img130.imageshack.us/img130/8742/18948898.gif

The sound wave from T is picked up by a receiver (R).

The transmitter & receiver have resonant frequency somewhere between 38 kHz to 42 kHz. Once we set the the signal generator to the resonant frequency, at which amplitude the wave length $$\lambda$$ of the sound can be measured this way: first adjust the position of R so that the two waves displayed on the oscilloscope are in phase ; second shif R backward or forward until the two waves are back in phase; third since R must have traveled by $$\lambda$$ to bring the two waves back in phase, the difference between the initial and final position of R is equal to one $$\lambda$$.

(i) Come up with a systematic method to measure the wave length $$\lambda$$.

(ii) Find the velocity using $$v=\lambda f$$. Then list as many systematic errors as you can.

The Attempt at a Solution

(i) What is it meant by a "systematic method" for measuring the wave length? Is it reffering to an accurate way of measuring it (like repeating the experiment a few times and averaging the results)?

(ii) I think the systematic errors in this experiment are related to the systematic errors in measuring the wave length. But I don't know what those errors might be ...

What systematic error is the most significant?

 

[roam]

Any suggestions guys?