diff --git a/src/tests/build.tests b/src/tests/build.tests
index f736572..eefceb9 100644
--- a/src/tests/build.tests
+++ b/src/tests/build.tests
@@ -25,9 +25,14 @@ then
             fi
         done
 
+        case "${TEST}" in
+        obj/tests/manip) TEST_EXTRAS="-lm" ;;
+        *) TEST_EXTRAS="" ;;
+        esac
+
         if [ ${MODIFIED} -ne 0 ]
         then
-            do_cmd ${CC} -Iobj ${CFLAGS} -o ${TEST} ${SRC} ${LIBS} ${EXTRAS} || return 1
+            do_cmd ${CC} -Iobj ${CFLAGS} -o ${TEST} ${SRC} ${LIBS} ${EXTRAS} ${TEST_EXTRAS} || return 1
             print_success "Built ${TEST}"
         else
             print_success "${TEST} is up to date"
diff --git a/src/tests/manip.c b/src/tests/manip.c
new file mode 100644
index 0000000..61fab4c
--- /dev/null
+++ b/src/tests/manip.c
@@ -0,0 +1,299 @@
+/* libiso8601/src/tests/manip.c
+ *
+ *  (c)2007, Laurence Withers, <l@lwithers.me.uk>.
+ *  Released under the GNU GPLv2. See file COPYING or
+ *  http://www.gnu.org/copyleft/gpl.html for details.
+*/
+
+#include "iso8601.h"
+
+#include <math.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+
+/* safe_strtod()
+ *  Converts `str' into a double, which it will store in `out'. If an error occurs, returns -1,
+ *  else 0 on success.
+ */
+int safe_strtod(const char* str, double* out)
+{
+    char* endp = 0;
+
+    errno = 0;
+    *out = strtod(str, &endp);
+    if(errno || !endp || *endp) return -1;
+
+    return 0;
+}
+
+
+
+/* date_stack
+ *  We use a stack of dates and/or periods to implement effectively an RPN manipulator.
+ */
+enum date_stack_type {
+    date_stack_type_date,
+    date_stack_type_per
+};
+
+struct date_stack {
+    enum date_stack_type type;
+
+    union {
+        struct {
+            struct iso8601_date d;
+            struct iso8601_details det;
+        }date;
+
+        struct iso8601_elapsed per;
+    }u;
+
+    struct date_stack* next;
+};
+
+struct date_stack* date_stack_top = 0;
+int date_stack_size = 0;
+
+
+
+/* date_stack_push_*()
+ *  Routines for pushing an object onto the date stack.
+ */
+void date_stack_push_date(const struct iso8601_date* d, const struct iso8601_details* det)
+{
+    struct date_stack* s;
+
+    s = malloc(sizeof(struct date_stack));
+    s->type = date_stack_type_date;
+    s->u.date.d = *d;
+    s->u.date.det = *det;
+    s->next = date_stack_top;
+
+    date_stack_top = s;
+    ++date_stack_size;
+}
+
+void date_stack_push_elapsed(const struct iso8601_elapsed* per)
+{
+    struct date_stack* s;
+
+    s = malloc(sizeof(struct date_stack));
+    s->type = date_stack_type_per;
+    s->u.per = *per;
+    s->next = date_stack_top;
+
+    date_stack_top = s;
+    ++date_stack_size;
+}
+
+
+
+/* date_stack_pop_date()
+ *  Pops a date from the stack, returning non-0 on error (underflow or type mismatch).
+ */
+int date_stack_pop_date(struct iso8601_date* d, struct iso8601_details* det)
+{
+    struct date_stack* next;
+
+    if(!date_stack_top) {
+        fputs("Stack underflow.\n", stderr);
+        return -1;
+    }
+    if(date_stack_top->type != date_stack_type_date) {
+        fputs("Type mismatch.\n", stderr);
+        return -1;
+    }
+
+    *d = date_stack_top->u.date.d;
+    *det = date_stack_top->u.date.det;
+
+    --date_stack_size;
+    next = date_stack_top->next;
+    free(date_stack_top);
+    date_stack_top = next;
+
+    return 0;
+}
+
+
+
+/* date_stack_pop_elapsed()
+ *  Pops an elapsed period from the stack, returning non-0 on error (underflow or type mismatch).
+ */
+int date_stack_pop_elapsed(struct iso8601_elapsed* per)
+{
+    struct date_stack* next;
+
+    if(!date_stack_top) {
+        fputs("Stack underflow.\n", stderr);
+        return -1;
+    }
+    if(date_stack_top->type != date_stack_type_per) {
+        fputs("Type mismatch.\n", stderr);
+        return -1;
+    }
+
+    *per = date_stack_top->u.per;
+
+    --date_stack_size;
+    next = date_stack_top->next;
+    free(date_stack_top);
+    date_stack_top = next;
+
+    return 0;
+}
+
+
+
+/* usage()
+ *  Displays help.
+ */
+void usage(void)
+{
+    fputs("Push a date or elapsed time onto the stack by entering it, e.g.:\n"
+        "   2007-07-29      12345.67\n"
+        "Operators:\n"
+        "   +   (date, period)      Advance date by elapsed time, push date.\n"
+        "   -   (date, period)      Regress date by elapsed time, push date.\n"
+        "   <   (date, date)        Prints 1 if first date less than second.\n"
+        "   <=  (date, date)        Prints 1 if first date less than or equal to second.\n"
+        "   ==  (date, date)        Prints 1 if dates equal.\n"
+        "   p   (date)              Prints a date.\n"
+        "\n"
+        "Type help for this screen at any point.\n"
+    "\n", stdout);
+}
+
+
+
+int parse_command(char* cmd)
+{
+    struct iso8601_date date, date2;
+    struct iso8601_details details, details2;
+    struct iso8601_elapsed period;
+    double period_d;
+    char date_str[40];
+
+    int ret = 0;
+
+    cmd = strtok(cmd, " \n");
+    while(cmd) {
+        if(!iso8601_parse(cmd, &date, 0, &details)) {
+            date_stack_push_date(&date, &details);
+
+        } else if(!safe_strtod(cmd, &period_d) && period_d >= 0) {
+            period.sec = trunc(period_d);
+            period.nsec = trunc((period_d - period.sec) * 1e9);
+            date_stack_push_elapsed(&period);
+
+        } else if(!strcmp(cmd, "+")) {
+            if(date_stack_pop_elapsed(&period) || date_stack_pop_date(&date, &details)) {
+                ret = 1;
+
+            } else {
+                iso8601_add_elapsed(&date, &period);
+                date_stack_push_date(&date, &details);
+            }
+
+        } else if(!strcmp(cmd, "-")) {
+            if(date_stack_pop_elapsed(&period) || date_stack_pop_date(&date, &details)) {
+                ret = 1;
+
+            } else {
+                iso8601_subtract_elapsed(&date, &period);
+                date_stack_push_date(&date, &details);
+
+            }
+
+        } else if(!strcmp(cmd, "<")) {
+            if(date_stack_pop_date(&date, &details) || date_stack_pop_date(&date2, &details2)) {
+                ret = 1;
+
+            } else {
+                printf("%d\n", iso8601_lt(&date2, &date));
+
+            }
+
+        } else if(!strcmp(cmd, "<=")) {
+            if(date_stack_pop_date(&date, &details) || date_stack_pop_date(&date2, &details2)) {
+                ret = 1;
+
+            } else {
+                printf("%d\n", iso8601_lte(&date2, &date));
+
+            }
+
+        } else if(!strcmp(cmd, "==")) {
+            if(date_stack_pop_date(&date, &details) || date_stack_pop_date(&date2, &details2)) {
+                ret = 1;
+
+            } else {
+                printf("%d\n", iso8601_eq(&date2, &date));
+
+            }
+
+        } else if(!strcmp(cmd, "p")) {
+            if(date_stack_pop_date(&date, &details)) {
+                ret = 1;
+
+            } else {
+                iso8601_print(date_str, sizeof(date_str), &date, &details);
+                fputs(date_str, stdout);
+                putc('\n', stdout);
+            }
+
+        } else {
+            fputs("Unrecognised command or argument.\n", stderr);
+            ret = 1;
+
+        }
+        
+        cmd = strtok(0, " \n");
+    }
+
+    return ret;
+}
+
+
+
+int main(int argc, char* argv[])
+{
+    int ret = 0;
+    char* buf = 0;
+    size_t buf_len = 0;
+
+    if(argc == 2 && !strcmp(argv[1], "--print-summary")) {
+        printf("Interactive date manipulator. Also evaluates commandline.\n");
+        return 0;
+    }
+
+    /* commandline -- evaluate arguments as though interactive */
+    if(argc > 1) {
+        for(ret = 1; ret < argc; ++ret) {
+            if(parse_command(argv[ret])) return 1;
+        }
+        return 0;
+    }
+
+    usage();
+    while(!feof(stdin)) {
+        printf("%d >> ", date_stack_size);
+        ret = getline(&buf, &buf_len, stdin);
+        if(ret == -1) break;
+
+        parse_command(buf);
+    }
+
+    return 0;
+}
+
+
+
+/* options for text editors
+kate: replace-trailing-space-save true; space-indent true; tab-width 4;
+vim: expandtab:ts=4:sw=4
+*/