Bruce, I've noticed that my weekly SMA is a lot different than two other charting systems I use.  They are all set to the log function, yet TC2000 is reporting a different number for SPY as an example.  

What causes this?

The calculations of simple moving averages is, well, simple. It is also quite standardized, so the possibilities are limited.

One possibility is that the other software is using different weeks. We use calendar weeks running from Monday through Friday for stocks in v12. Note that this means the moving average would be different in v7 where we use rolling 5 trading day weeks instead.

Another possibility is that the moving average is of something other than price such as a another moving average. You could try removing and re-adding the moving average and making sure it is getting added to price instead of something else.

Another possibility would be that the other software might be plotting a daily moving average on the weekly chart. While this seems doubtful, I have seen situations where all of the moving averages in a program are daily even when changing the time frame of the chart.

Thank you.

You're welcome.