diff --git a/cxx/mcc_mount_pec.h b/cxx/mcc_mount_pec.h
index 2dcb442..94548b9 100644
--- a/cxx/mcc_mount_pec.h
+++ b/cxx/mcc_mount_pec.h
@@ -5,21 +5,92 @@
 namespace mcc
 {
 
+enum class MccMountPECType { PEC_TYPE_GEOMETRY, PEC_TYPE_GEOMETRY_BSPLINE, PEC_TYPE_BSPLINE };
+
+template <MccMountPECType TYPE = MccMountPECType::PEC_TYPE_GEOMETRY>
 class MccMountPEC
 {
 public:
+    static constexpr MccMountPECType pecType = TYPE;
+
     struct pec_result_t {
         MccAngle dx, dy;
     };
 
+    // "classic" geometric PEC coefficients
+    struct pec_geom_coeffs_t {
+        typedef double coeff_t;
+
+        coeff_t zeroPointX;
+        coeff_t zeroPointY;
+        coeff_t collimationErr;  // tube collimation error
+        coeff_t nonperpendErr;   // X-Y axes nonperpendicularity
+        coeff_t misalignErr1;    // misalignment of hour-angle/azimuth axis: left-right for equatorial, East-West for
+                                 // alt-azimuthal
+        coeff_t misalignErr2;    // misalignment of hour-angle/azimuth axis: vertical for equatorial, North-South for
+                                 // alt-azimuthal
+
+        coeff_t tubeFlexure;
+        coeff_t forkFlexure;
+        coeff_t DECaxisFlexure;  // declination axis flexure
+    };
+
+    // B-splines coefficients
+    struct pec_bspline_coeffs_t {
+        typedef double knot_t;
+        typedef double coeff_t;
+
+        std::vector<knot_t> knots;
+        std::vector<coeff_t> coeffs;
+    };
+
+
+    MccMountPEC(pec_geom_coeffs_t geom_coeffs, pec_bspline_coeffs_t bspline_coeffs)
+        requires(TYPE == MccMountPECType::PEC_TYPE_GEOMETRY_BSPLINE)
+        : _geomCoeffs(std::move(geom_coeffs)), _bspleCoeffs(std::move(bspline_coeffs))
+    {
+    }
+
+    MccMountPEC(pec_geom_coeffs_t geom_coeffs)
+        requires(TYPE == MccMountPECType::PEC_TYPE_GEOMETRY)
+        : _geomCoeffs(std::move(geom_coeffs)), _bspleCoeffs()
+    {
+    }
+
+
+    MccMountPEC(pec_bspline_coeffs_t bspline_coeffs)
+        requires(TYPE == MccMountPECType::PEC_TYPE_BSPLINE)
+        : _geomCoeffs(), _bspleCoeffs(std::move(bspline_coeffs))
+    {
+    }
+
+
+    // X and Y axis encoder coordinates
     template <std::derived_from<MccAngle> XT, std::derived_from<MccAngle> YT>
     pec_result_t compute(const XT& x, const YT& y)
     {
         static constexpr MccCoordPairKind coord_kind = traits::mcc_type_pair_hash<XT, YT>();
 
-        pec_result_t res;
+        pec_result_t res{0.0, 0.0};
 
         if constexpr (coord_kind == MccCoordPairKind::COORDS_KIND_HADEC_APP) {
+            if constexpr (TYPE == MccMountPECType::PEC_TYPE_GEOMETRY) {
+                const auto tanY = std::tan(y);
+                const auto sinX = std::sin(x);
+                const auto cosX = std::cos(x);
+
+                res.dx = _geomCoeffs.zeroPointX + _geomCoeffs.collimationErr / std::cos(y) +
+                         _geomCoeffs.nonperpendErr * tanY - _geomCoeffs.misalignErr1 * cosX * tanY +
+                         _geomCoeffs.misalignErr2 * sinX * tanY;
+
+                res.dy = _geomCoeffs.zeroPointY + _geomCoeffs.misalignErr1 * sinX + _geomCoeffs.misalignErr2 * cosX;
+            }
+
+            if constexpr (TYPE == MccMountPECType::PEC_TYPE_BSPLINE ||
+                          TYPE == MccMountPECType::PEC_TYPE_GEOMETRY_BSPLINE) {
+                res.dx += 0.0;
+                res.dy += 0.0;
+            }
         } else if constexpr (coord_kind == MccCoordPairKind::COORDS_KIND_AZALT) {
         } else {
             static_assert(false, "UNSUPPORTED");
@@ -27,6 +98,10 @@ public:
 
         return res;
     }
+
+private:
+    pec_geom_coeffs_t _geomCoeffs;
+    pec_bspline_coeffs_t _bspleCoeffs;
 };
 
 }  // namespace mcc