DOB is a feature found on the Sanderson Accu-Tuner III and IV.    (See: Page 30 of the 2011 SAT IV Instruction Manual.)

DOB allows the technician to expand or contract the stretch of the memory tuning and can be used where ever more or less stretch is needed.

DOB does not affect A4 but does affect every other note on the piano.

A positive DOB setting increases the stretch of the memory tuning by raising the notes above A4 and lowering the notes below A4.

A negative DOB setting reduces the stretch of the memory tuning by raising all notes below A4 and lowering all notes above A4.

DOB is an adjustment of the double octave’s beat rate, in tenths of a beat.

A .1 DOB setting increases the stretch, widening the double octaves by .1 beat per second.
A .5 DOB setting will increase the beat rate of the double octaves beat by about ½ bps.

The maximum DOB setting (positive or negative) is 2.0 which increases or decreases the widths of the double octaves by 2 beats per second.

When using any memory tuning template with the Sanderson Accu-Tuner III or IV,  DOB makes it possible to modify the stretch ‘on the fly’,
anywhere in the scale, during the tuning process.

Here are a few guidelines as to how much DOB will affect the placement of A3 and A5 (in cents):

.1 (of a beat) DOB @ A5 (or A3) will move A5 (or A3) .2 cents.

.1 (of a beat) DOB @ A2 (or A6) will move A2 (or A6) .4 cents.

.1 (of a beat) DOB @ A7 will move A7  .6 cents.

.1 (of a beat) DOB @ A0 will move A0  .8 cents.

It is best to add or remove DOB incrementally to keep the tuning as smooth as possible.   The cents buttons can be used to even further smooth out
any DOB ‘hiccups’ on notes above and below the roll off.