diff --git a/Makefile b/Makefile
index 9e158c9..7443d80 100644
--- a/Makefile
+++ b/Makefile
@@ -7,8 +7,11 @@ all:		testbed
 genplotting.o:	genplotting.f90 Makefile
 	gfortran -Wall -c $< 
 
-testbed:	testbed.f90 Makefile genplotting.o
-	gfortran -Wall $< genplotting.o -o $@
+genp_tests.o:	genp_tests.f90 genplotting.o Makefile
+	gfortran -Wall -c $< 
+
+testbed:	testbed.f90 Makefile genp_tests.o genplotting.o
+	gfortran -Wall $< genplotting.o genp_tests.o -o $@
 
 # -----------------------------------------------
 
diff --git a/genp_tests.f90 b/genp_tests.f90
new file mode 100644
index 0000000..84fd313
--- /dev/null
+++ b/genp_tests.f90
@@ -0,0 +1,41 @@
+!
+!           MODULE FOR TESTING THE GENPLOTTING MODULE
+!
+! this crapware is released by tTh under the
+!             DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
+!
+! new Sun May 17 11:21:39 AM UTC 2026
+
+module genp_tests
+  use genplotting
+  implicit none
+  contains
+! ---------------------------------------------------------
+subroutine genp_test_rotation()
+
+  real             :: mat(3, 3)
+  real             :: pta(3), ptb(3)
+  integer                :: pass, i, j
+  
+  write(0, '("*** TEST ROTATION ***")' )
+  do pass=1, 90
+    call genp_set_rotation (real(pass)*0.10)
+    write(0, *) "  * the matrix was : "
+    call genp_get_rot_matrix(mat)
+    do i=1, 3
+      do j=1, 3
+        write (0, '("   ", F8.5)', advance='no') mat(i,j)
+      end do
+      write(0, *)
+    end do
+
+    call genp_move(0.0, 0.0)
+    pta(1) = 11.0   ;   pta(2) = 0.0   ;   pta(3) = 0.0
+    ptb = matmul(mat, pta)
+    write(0, '(" got XY: ", F8.5, " ", F8.5)') ptb(1), ptb(2)
+    call genp_draw(ptb(1), ptb(2), 1+mod(pass, 7))
+  end do   ! pass
+
+end subroutine
+! ---------------------------------------------------------
+end module
diff --git a/genplotting.f90 b/genplotting.f90
index 05cad12..753072a 100644
--- a/genplotting.f90
+++ b/genplotting.f90
@@ -11,8 +11,9 @@ module genplotting
   real      ::    xoffset, yoffset, xscale, yscale
   private   ::    xoffset, yoffset, xscale, yscale
 
-  real      ::    rotation
-  private   ::    rotation
+  real      ::    rotation, rotmatrix(3,3)
+  private   ::    rotation, rotmatrix, compute_rot_matrix
+  private   ::    print_rot_matrix
 
   integer   ::    outunit = 6
   private   ::    outunit
@@ -21,7 +22,7 @@ contains
 ! ---------------------------------------------------------
 ! the first parameter _must_ be 0.
 ! the second can be
-!    - the name of a file for recoding plot instructions
+!    - the name of a file for recording plot instructions
 !  or
 !    - an empty string for send plot command to stdout
 !
@@ -44,6 +45,7 @@ subroutine genp_init (foo, fname)
   ymin = 9e9       ;       ymax = -9e9
   xoffset = 0.0    ;       yoffset = 0.0
   xscale  = 1.0    ;       yscale  = 1.0
+
   rotation = 0.0
 
 end subroutine
@@ -67,6 +69,56 @@ subroutine genp_get_scale(sx, sy)
   sx = xscale      ;      sy = yscale
 end subroutine
 ! ---------------------------------------------------------
+! this is a private procedure, don't call it from your prog
+subroutine compute_rot_matrix(angle)
+  real, intent(in)    :: angle
+  write (0, '("compute rot matrix for", F8.5, " radians")') &
+                                     angle
+  rotmatrix (1, 1) =  cos(angle)
+  rotmatrix (1, 2) =  sin(angle)
+  rotmatrix (1, 3) =  0.0
+
+  rotmatrix (2, 1) = -sin(angle)
+  rotmatrix (2, 2) =  cos(angle)
+  rotmatrix (2, 3) =  0.0
+
+  rotmatrix (3, 1) =  0.0
+  rotmatrix (3, 2) =  0.0
+  rotmatrix (3, 3) =  1.0
+
+end subroutine
+!                  -----------------
+!    we have computed some fancy numbers
+!                      and we want to see them !
+subroutine print_rot_matrix(fd)
+  integer, intent(in)    :: fd
+
+  integer                :: i, j
+  do i=1, 3
+    do j=1, 3
+      write (fd, '("   ", F8.5)', advance='no') rotmatrix(i,j)
+    end do
+    write(fd, *)
+  end do
+end subroutine
+! ---------------------------------------------------------
+subroutine genp_set_rotation(angle)
+  real, intent(in)     :: angle
+  rotation = angle
+  !       compute the matrix here !
+  call compute_rot_matrix(angle)
+  ! call print_rot_matrix(0)
+end subroutine
+
+real function genp_get_rotation()
+  genp_get_rotation = rotation
+end function
+
+subroutine genp_get_rot_matrix (dst)
+  real, intent(out)   :: dst(3, 3)
+  dst = rotmatrix
+end subroutine
+! ---------------------------------------------------------
 subroutine genp_move (px, py)
   real, intent(in)        :: px, py
   real                    :: lx, ly
@@ -138,7 +190,7 @@ end subroutine
 subroutine genp_end (foo)
   integer, intent(in)    :: foo
 
-  write (0, '("--- genp_end ---")')
+  write (0, '("------------- genp_end -------------")')
   write (0, '("minmax X ", 2F18.5)') xmin, xmax
   write (0, '("minmax Y ", 2F18.5)') ymin, ymax
 
diff --git a/testbed.f90 b/testbed.f90
index 634b171..4d7b43d 100644
--- a/testbed.f90
+++ b/testbed.f90
@@ -1,23 +1,18 @@
+!
+!           TESTBED FOR GENPLOTTING90
+!
+! this crapware is released by tTh under the
+!             DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
+!
+
 program testbed
   use genplotting
+  use genp_tests
   implicit none
 
-  integer     idx
-  real        fdx, xp, yp, scx, scy
-
   call genp_init(0, "foo.scratch")
-  scx = 0.8   ;   scy = 1.5
-  do idx=5, 60
-    fdx = real(idx)
-    xp = 3.5 * cos((fdx/14.0)-0.7)
-    yp = 3.5 * sin((fdx/10.0)+0.3)
-    call genp_set_offset(xp, yp)
-    call genp_set_scale(scx, scy)
-    call genp_circle(fdx, 60, 1+mod(idx, 3))
-    scx = scx + 0.0075
-    scy = scy - 0.0075
-  enddo
+  call genp_test_rotation()
+  ! call genp_plot_axes(5.1)
   call genp_end(0)
-  call genp_do_render("foo.scratch", "foo.tga", 512, 512)
 
 end program