I would be interested to see how the post frequency is growing monthly or some such.

We've not seen any difference in their frequency since we went to self-showings.

That is why a pipeline gets filled with a process in different stages of buying and selling to increase frequency of closed sales and transactions over time.Good luck.

Did get one call that said "your letter is distasteful"So what is everyone doing in their direct mailings...what is the frequency...when should I send the second round?

Although, this would differ from county to county, but the indicator assumed that influences in the frequency and speed of transactions between buyer and seller to be the fundamental basis of property taxation based from speculative land valuation formula.  

The key is to make sure you're doing enough VOLUME (i.e. 2,000 per month) and that you repeatedly hit the list (FREQUENCY).Your expectations on your first 2 mailings should be ZERO leads.

The optimal frequency with which to send out your letters and your ROR will be something unique to your market.

On another note from the aviation world.. the Austin Center had their computers in the basement.. basement flooded  ATC went down... so you had the airlines having to resort to flying like little guys.. flying VFR patterns and calling out their postions on the common radio frequencies which is NOT very common for them.Also departures were old school once an airliner was in the que and number one for take off they had to get on their cell phones and call Houston center for their IFR clearance.. this is what happens in non radar environments.. but its a testament to our aviation system that when tech goes down we can keep flying.. albeit like its 1950 but we keep going

Beware.I suspect this is whats driving the frequency and stratospheric heights of 1st note increases. 

Next decide, what you will be mailing and the frequency.