diff --git a/base/mp_coretable.sas b/base/mp_coretable.sas
index d0eca56..1de4c43 100644
--- a/base/mp_coretable.sas
+++ b/base/mp_coretable.sas
@@ -10,6 +10,8 @@
       %mp_coretable(LOCKTABLE,libds=work.locktable)
 
   @param [in] table_ref The type of table to create.  Example values:
+    @li DIFFTABLE - Used to store changes to tables.  Used by mp_storediffs.sas
+      and mp_stackdiffs.sas
     @li FILTER_DETAIL - For storing detailed filter values.  Used by
       mp_filterstore.sas.
     @li FILTER_SUMMARY - For storing summary filter values.  Used by
@@ -25,6 +27,8 @@
   @li mp_filterstore.sas
   @li mp_lockanytable.sas
   @li mp_retainedkey.sas
+  @li mp_storediffs.sas
+  @li mp_stackdiffs.sas
 
   @version 9.2
   @author Allan Bowe
@@ -36,7 +40,29 @@
 %local outds ;
 %let outds=%sysfunc(ifc(&libds=0,_data_,&libds));
 proc sql;
-%if &table_ref=LOCKTABLE %then %do;
+%if &table_ref=DIFFTABLE %then %do;
+  create table &outds(
+      load_ref char(36) label='unique load reference',
+      processed_dttm num format=E8601DT26.6 label='Processed at timestamp',
+      libref char(8) label='Library Reference (8 chars)',
+      dsn char(32) label='Dataset Name (32 chars)',
+      key_hash char(32) label=
+        'MD5 Hash of primary key values (pipe seperated)',
+      move_type char(1) label='Either (A)ppended, (D)eleted or (M)odified',
+      is_pk num label='Is Primary Key Field? (1/0)',
+      is_diff num label=
+        'Did value change? (1/0/-1).  Always -1 for appends and deletes.',
+      tgtvar_type char(1) label='Either (C)haracter or (N)umeric',
+      tgtvar_nm char(32) label='Target variable name (32 chars)',
+      oldval_num num format=best32. label='Old (numeric) value',
+      newval_num num format=best32. label='New (numeric) value',
+      oldval_char char(32765) label='Old (character) value',
+      newval_char char(32765) label='New (character) value',
+    constraint pk_mpe_audit
+      primary key(load_ref,libref,dsn,key_hash,tgtvar_nm)
+  );
+%end;
+%else %if &table_ref=LOCKTABLE %then %do;
   create table &outds(
       lock_lib char(8),
       lock_ds char(32),
diff --git a/base/mp_stackdiffs.sas b/base/mp_stackdiffs.sas
new file mode 100644
index 0000000..a6da2be
--- /dev/null
+++ b/base/mp_stackdiffs.sas
@@ -0,0 +1,224 @@
+/**
+  @file
+  @brief Prepares an audit table for stacking (re-applying) the changes.
+  @details WORK IN PROGRESS!!
+
+    When the underlying data from a Base Table is refreshed, it can be helpful
+    to have any previously-applied changes, re-applied.
+
+    Such situation might arise if you are applying those changes using a tool
+    like [Data Controller for SAS®](https://datacontroller.io) - which records
+    all such changes in an audit table.
+    It may also apply if you are preparing a series of specific cell-level
+    transactions, that you would like to apply to multiple sets of (similarly
+    structured) Base Tables.
+
+    In both cases, it is necessary that the transactions are stored using
+    the mp_storediffs.sas macro, or at least that the underlying table is
+    structured as per the definition in mp_coretable.sas (DIFFTABLE entry)
+
+    <b>This</b> macro is used to convert the stored changes (tall format) into
+    staged changes (wide format), with base table values incorporated (in the
+    case of modified rows), ready for the subsequent load process.
+
+    Essentially then, what this macro does, is turn a table like this:
+
+  |LIBREF:$8.|DSN:$32.|MOVE_TYPE:$1.|TGTVAR_NM:$32.|IS_PK:best.|IS_DIFF:best.|TGTVAR_TYPE:$1.|OLDVAL_NUM:best32.|NEWVAL_NUM:best32.|OLDVAL_CHAR:$32765.|NEWVAL_CHAR:$32765.|
+  |---|---|---|---|---|---|---|---|---|---|---|
+  |`SASHELP `|`CLASS `|`A `|`NAME `|`1 `|`-1 `|`C `|`. `|`. `|` `|`Newbie `|
+  |`SASHELP `|`CLASS `|`A `|`AGE `|`0 `|`-1 `|`N `|`. `|`13 `|` `|` `|
+  |`SASHELP `|`CLASS `|`A `|`HEIGHT `|`0 `|`-1 `|`N `|`. `|`65.3 `|` `|` `|
+  |`SASHELP `|`CLASS `|`A `|`SEX `|`0 `|`-1 `|`C `|`. `|`. `|` `|`F `|
+  |`SASHELP `|`CLASS `|`A `|`WEIGHT `|`0 `|`-1 `|`N `|`. `|`98 `|` `|` `|
+  |`SASHELP `|`CLASS `|`D `|`NAME `|`1 `|`-1 `|`C `|`. `|`. `|`Alfred `|` `|
+  |`SASHELP `|`CLASS `|`D `|`AGE `|`0 `|`-1 `|`N `|`14 `|`. `|` `|` `|
+  |`SASHELP `|`CLASS `|`D `|`HEIGHT `|`0 `|`-1 `|`N `|`69 `|`. `|` `|` `|
+  |`SASHELP `|`CLASS `|`D `|`SEX `|`0 `|`-1 `|`C `|`. `|`. `|`M `|` `|
+  |`SASHELP `|`CLASS `|`D `|`WEIGHT `|`0 `|`-1 `|`N `|`112.5 `|`. `|` `|` `|
+  |`SASHELP `|`CLASS `|`M `|`NAME `|`1 `|`0 `|`C `|`. `|`. `|`Alice `|`Alice `|
+  |`SASHELP `|`CLASS `|`M `|`AGE `|`0 `|`1 `|`N `|`13 `|`99 `|` `|` `|
+  |`SASHELP `|`CLASS `|`M `|`HEIGHT `|`0 `|`0 `|`N `|`56.5 `|`56.5 `|` `|` `|
+  |`SASHELP `|`CLASS `|`M `|`SEX `|`0 `|`0 `|`C `|`. `|`. `|`F `|`F `|
+  |`SASHELP `|`CLASS `|`M `|`WEIGHT `|`0 `|`0 `|`N `|`84 `|`84 `|` `|` `|
+
+    Into three tables like this:
+
+  <b> `work.outmod`: </b>
+  |NAME:$8.|SEX:$1.|AGE:best.|HEIGHT:best.|WEIGHT:best.|
+  |---|---|---|---|---|
+  |`Alice `|`F `|`99 `|`56.5 `|`84 `|
+
+  <b> `work.outadd`: </b>
+  |NAME:$8.|SEX:$1.|AGE:best.|HEIGHT:best.|WEIGHT:best.|
+  |---|---|---|---|---|
+  |`Newbie `|`F `|`13 `|`65.3 `|`98 `|
+
+  <b> `work.outdel`: </b>
+  |NAME:$8.|SEX:$1.|AGE:best.|HEIGHT:best.|WEIGHT:best.|
+  |---|---|---|---|---|
+  |`Alfred `|`M `|`14 `|`69 `|`112.5 `|
+
+    As you might expect, there are a bunch of extra features and checks.
+
+    The macro supports both SCD2 (TXTEMPORAL) and UPDATE loadtypes. If the
+    base table contains a PROCESSED_DTTM column (or similar), this can be
+    ignored by declaring it in the `processed_dttm_var` parameter.
+
+    If the structure of the Base Table has changed, the following rules apply:
+
+    @li New Columns - Irrelevant for deletes.  For inserts, the new column
+      values are set to missing. For updates, the base table values are used.
+    @li Deleted Columns - These will also be absent in the output tables.
+    @li Change in Primary Key - This is not (well, cannot be) supported!!
+
+    Rules for stacking changes are as follows:
+
+    <table>
+    <tr><th>Transaction Type</th><th>Behaviour</th></tr>
+    <tr>
+      <td>Deletes</td>
+      <td>
+        For previously deleted rows, the PK is added to the `outDEL` table<br>
+        If the row no longer exists in the base table, the row is added to the
+        `errDS` table instead.
+      </td>
+    </tr>
+    <tr>
+      <td>Inserts</td>
+      <td>
+        Previously newly added rows are added to the `outADD` table UNLESS they
+        are present in the Base table.<br>In this case they are added to the
+        `errDS` table instead.
+      </td>
+    </tr>
+    <tr>
+      <td>Updates</td>
+      <td>
+        Previously modified rows are merged with base table values such that
+        only the individual cells that were _previously_ changed are re-applied.
+        Where the row contains cells that were not marked as having changed in
+        the prior transaction, the 'blanks' are filled with base table values in
+        the `outMOD` table.<br>
+        If the row no longer exists on the base table, then the row is added to
+        the `errDS` table instead.
+      </td>
+    </tr>
+    </table>
+
+    To illustrate the above with a diagram:
+
+    @dot
+      digraph {
+        rankdir="TB"
+
+        start[label="Transaction Type?" shape=Mdiamond]
+        del[label="Base Row Exists?" shape=rectangle]
+        add [label="Base Row Exists?" shape=rectangle]
+        mod [label="Base Row Exists?" shape=rectangle]
+        outmod [label="outMOD Table" shape=box3d]
+        outadd [label="outADD Table" shape=box3d]
+        outdel [label="outDEL Table" shape=box3d]
+        outerr [label="ErrDS Table" shape=box3d]
+        start -> del [label="Delete"]
+        start -> add [label="Insert"]
+        start -> mod [label="Update"]
+
+        del -> outdel [label="Yes"]
+        del -> outerr [label="No" color="Red" fontcolor="Red"]
+        add -> outadd [label="Yes"]
+        add -> outerr [label="No" color="Red" fontcolor="Red"]
+        mod -> outerr [label="Yes" color="Red" fontcolor="Red"]
+        mod -> outmod [label="No"]
+
+      }
+    @enddot
+
+    For examples of usage, check out the mp_stackdiffs.test.sas program.
+
+
+  @param [in] baselibds Base Table against which the changes will be applied,
+    in libref.dataset format.
+  @param [in] auditlibds Dataset with previously applied transactions, to be
+    re-applied. Use libref.dataset format.
+    DDL as follows:  %mp_coretable(DIFFTABLE)
+  @param [in] key Space seperated list of key variables
+  @param [in] mdebug= Set to 1 to enable DEBUG messages and preserve outputs
+  @param [in] processed_dttm_var= (0) If a variable is being used to mark
+    the processed datetime, put the name of the variable here.  It will NOT
+    be included in the staged dataset (the load process is expected to
+    provide this)
+  @param [out] errds= (work.errds) Output table containing problematic records.
+    The columns of this table are:
+    @li PK_VARS - Space separated list of primary key variable names
+    @li PK_VALS - Slash separted list of PK variable values
+    @li ERR_MSG - Explanation of why this record is problematic
+  @param [out] outmod= (work.outmod) Output table containing modified records
+  @param [out] outadd= (work.outadd) Output table containing additional records
+  @param [out] outdel= (work.outdel) Output table containing deleted records
+
+
+  <h4> SAS Macros </h4>
+  @li mf_getuniquename.sas
+  @li mf_islibds.sas
+  @li mp_abort.sas
+
+
+  <h4> Related Macros </h4>
+  @li mp_coretable.sas
+  @li mp_storediffs.sas
+
+  @version 9.2
+  @author Allan Bowe
+**/
+/** @cond */
+
+%macro mp_stackdiffs(baselibds
+  ,auditlibds
+  ,key
+  ,mdebug=0
+  ,processed_dttm_var=0
+  ,errds=work.errds
+  ,outmod=work.outmod
+  ,outadd=work.outadd
+  ,outdel=work.outdel
+)/*/STORE SOURCE*/;
+%local dbg;
+%if &mdebug=1 %then %do;
+  %put &sysmacroname entry vars:;
+  %put _local_;
+%end;
+%else %let dbg=*;
+
+/* input parameter validations */
+%mp_abort(iftrue= (%mf_islibds(&baselibds) ne 1)
+  ,mac=&sysmacroname
+  ,msg=%str(Invalid baselibds: &baselibds)
+)
+%mp_abort(iftrue= (%mf_islibds(&auditlibds) ne 1)
+  ,mac=&sysmacroname
+  ,msg=%str(Invalid auditlibds: &auditlibds)
+)
+%mp_abort(iftrue= (%length(&key)=0)
+  ,mac=&sysmacroname
+  ,msg=%str(Missing key variables!)
+)
+
+/* set up unique and temporary vars */
+%local ds1 ds2 ds3 ds4 hashkey inds_auto inds_keep dslist;
+%let ds1=%upcase(work.%mf_getuniquename(prefix=mpsd_ds1));
+%let ds2=%upcase(work.%mf_getuniquename(prefix=mpsd_ds2));
+%let ds3=%upcase(work.%mf_getuniquename(prefix=mpsd_ds3));
+%let ds4=%upcase(work.%mf_getuniquename(prefix=mpsd_ds4));
+%let hashkey=%upcase(%mf_getuniquename(prefix=mpsd_hashkey));
+%let inds_auto=%upcase(%mf_getuniquename(prefix=mpsd_inds_auto));
+%let inds_keep=%upcase(%mf_getuniquename(prefix=mpsd_inds_keep));
+
+%let key=%upcase(&key);
+
+%if &mdebug=0 %then %do;
+  proc sql;
+  drop table &ds1, &ds2, &ds3, &ds4;
+%end;
+
+%mend mp_stackdiffs;
+/** @endcond */
\ No newline at end of file
diff --git a/sasjs/doxy/Doxyfile b/sasjs/doxy/Doxyfile
index fcc2bd9..8e5b066 100644
--- a/sasjs/doxy/Doxyfile
+++ b/sasjs/doxy/Doxyfile
@@ -8,6 +8,7 @@ FILE_PATTERNS          = *.sas \
                          *.dox
 GENERATE_LATEX         = NO
 GENERATE_TREEVIEW      = YES
+HAVE_DOT               = YES
 HIDE_FRIEND_COMPOUNDS  = YES
 HIDE_IN_BODY_DOCS      = YES
 HIDE_SCOPE_NAMES       = YES