Radio Shack SPL Meter corrections

Looking at some other recent thread and some own experience, I have come to question the accuracy of the Radio Shack SPL meter and some of the suggested (measured?) correction curves. I was wondering what your experiences with the meter are and what correction curves you use.

I found the following different suggestions for correcting the meter readings:

Sean's Audiogon corrections

Audio Asylum corrections

The issue of the SPL meter corrections came up in a recent thread:

4khz-8khz room spike

From my own experiences, I have had similar observations (3-6 kHz plateau with 6dB or more). So far I had used the Asylum corrections but certainly Sean's corrections would lower this anomaly close to normal due to the 4dB difference between the two correction curves in that frequency range.

Another problem was that I found a significant high frequency roll-off (-10db or more) for frequencies above 12KHz. This roll-off was present and similar with several different speakers (Spendor S3/5, Mission 751, Omega Super3) and different electronics (Linn amps, Jolida tube amp). This would indicate a need for a correction of my SPL meter in that range as well. Measurements were done on a tripod, using the C-(neutral) weighting and slow response.

Any suggestions on the use of the SPL meter? What are the variations between different production dates of the SPL meter? Are there any, not too expensive (less than $300), alternatives? What about suggestions for a spectrum analyzer combined with a corrected microphone?

Thanks to everyone for their responses in advance. Also, many thanks to Sean and Clayton for posting the above corrections.