diff --git a/doc/source/functions.rst b/doc/source/functions.rst
index f24220eebf70269e4d46ec2d6fa61c4047b0e7fa..233f91140afd0c2ce13a2768d5d2a06ac65c9159 100644
--- a/doc/source/functions.rst
+++ b/doc/source/functions.rst
@@ -339,7 +339,7 @@ Detailed descriptions
    :param task_description: Description string.
    :type task_description: string
 
-.. function:: sumthreshold(data, xthreshold_f, ythreshold_f, include_x, include_y)
+.. function:: sumthreshold(data, x_threshold_factor, y_threshold_factor, x_direction, y_direction)
 
    Run the SumThreshold algorithm on the data. This algorithm detects sharp,
    line-shaped features in the time-frequency domain that are typical for RFI.
@@ -351,24 +351,25 @@ Detailed descriptions
    Lower values will detect more features. A reasonable value for the
    thresholds is 1.
    
-   The "include" parameters turn
-   detection in their particular directions on and off. Note that detection in
-   "x" (=time) direction means detection of contiguous high-power samples
+   The ``x_direction``/``y_direction`` parameters turn
+   detection in their particular directions on and off. If a direction is turned off, the
+   threshold factor for that direction is ignored. Note that detection in
+   *x*-direction (which is the time-direction) means detection of contiguous high-power samples
    in time, such as transmitters that occupy the same channel continuously.
-   The y-direction detection is sensitive to transient, broadband RFI.
+   The *y*-direction detection is sensitive to transient, broadband RFI.
 
-   :param data: The data (modified in place).
+   :param data: The data (modified in place)
    :type data: :class:`Data`
-   :param xthreshold_f: Threshold factor in time direction
-   :type xthreshold_f: number
-   :param ythreshold_f: Threshold factor in frequency direction
-   :type ythreshold_f: number
-   :param include_x: The data that is used as mask.
-   :type include_x: :class:`Data`
-   :param include_y: The data that is used as mask.
-   :type include_y: :class:`Data`
+   :param x_threshold_factor: Threshold factor in time direction
+   :type x_threshold_factor: number
+   :param y_threshold_factor: Threshold factor in frequency direction
+   :type y_threshold_factor: number
+   :param x_direction: Enable flagging in time direction
+   :type x_direction: boolean
+   :param y_direction: Enable flagging in frequency direction
+   :type y_direction: boolean
    
-.. function:: sumthreshold_masked(data, mask_data, x_threshold_f, y_threshold_f, x_direction, y_direction)
+.. function:: sumthreshold_masked(data, mask_data, x_threshold_factor, y_threshold_factor, x_direction, y_direction)
 
    Same as :meth:`sumthreshold`, but with a mask. Visibilities that are flagged
    in the mask are considered to be visibilities that have not been sampled and
@@ -378,15 +379,15 @@ Detailed descriptions
 
    :param data: The data (modified in place).
    :type data: :class:`Data`
-   :param mask_data: The data that is used as mask.
+   :param mask_data: The data that is used as mask
    :type mask_data: :class:`Data`
-   :param x_threshold_f: Threshold factor in time direction
-   :type x_threshold_f: number
-   :param y_threshold_f: Threshold factor in frequency direction
-   :type y_threshold_f: number
-   :param x_direction: The data that is used as mask.
+   :param x_threshold_factor: Threshold factor in time direction
+   :type x_threshold_factor: number
+   :param y_threshold_factor: Threshold factor in frequency direction
+   :type y_threshold_factor: number
+   :param x_direction: Enable flagging in time direction
    :type x_direction: boolean
-   :param y_direction: The data that is used as mask.
+   :param y_direction: Enable flagging in frequency direction
    :type y_direction: boolean
    
 .. function:: threshold_channel_rms(data, threshold, flag_low_outliers)