diff --git a/DESCRIPTION b/DESCRIPTION
index 93e1224..aba4c29 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -32,3 +32,4 @@ Suggests:
     covr
 LinkingTo: Rcpp
 RoxygenNote: 6.1.1
+Encoding: UTF-8
diff --git a/NAMESPACE b/NAMESPACE
index e78a9b5..5675bce 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -3,7 +3,6 @@
 S3method(plot,rudnicki.pt)
 export(.rudnicki_pt)
 export(.setleft)
-export(.surface_J_ringdisk)
 export(.surface_g)
 export(.surface_g_pdisk)
 export(.surface_g_pt)
@@ -43,6 +42,7 @@ export(surface_displacement)
 export(surface_displacement_point)
 export(surface_displacement_pressuredisk)
 export(surface_displacement_reservoir)
+export(surface_displacement_ringdisk)
 export(timevarying_fluidmass)
 export(timevarying_porepressure)
 export(timevarying_surface_displacement)
diff --git a/R/segall92.R b/R/segall92.R
index 0bcf252..3a5e495 100644
--- a/R/segall92.R
+++ b/R/segall92.R
@@ -1,43 +1,95 @@
-segall92 <- function(help=FALSE){
+#' @title Elastostatic subsidence of a half space
+#' 
+segall92 <- function(){
   cat("\nThis function is simply a placeholder. See the documentation ( `?segall92` ).\n")
-  if (help) ?segall92
 }
 
-#' @rdname segall92
-#' @export
-.surface_J_ringdisk <- function(x, ring.depth, radius, thickness){
-	
-	z_prime <- ring.depth
-	r <- x
-	r_prime <- radius
-	
+# Integral in the Green's function that must be integrated
+# @rdname segall92
+# @export
+.green_segall92 <- function(k., r., a., z_prime., radial. = TRUE){
+  # r radial observation point
+  # a radius of disk
+  # z_prime depth disk
+  # k vector along direction of integration (k >= 0)
+  ka <- k. * a.
+  kr <- k. * r.
+  kz <- k. * z_prime.
+  J0 <- Bessel::BesselJ(kr, 0)
+  J1 <- Bessel::BesselJ(kr, 1)
+  J1a <- Bessel::BesselJ(ka, 1)
+  E <- exp(-1 * kz)
+  if (radial.){
+    # radial displacements at the surface [ur(r,0)]
+    # Wang (2000) equation 9.29
+    J1 * J1a * E
+  } else {
+    # vertical displacements at the surface [uz(r,0)]
+    # Wang (2000) equation 9.30
+    J0 * J1 * E
+  }
 }
 
-	# Integral in the Green's function that must be integrated
-	.green_integ <- function(k., r., a., z_prime., radial. = TRUE){
-		# r radial observation point
-		# a radius of disk
-		# z_prime depth disk
-		# k vector along direction of integration (k >= 0)
-		ka <- k. * a.
-		kr <- k. * r.
-		kz <- k. * z_prime.
-		J0 <- Bessel::BesselJ(kr, 0)
-		J1 <- Bessel::BesselJ(kr, 1)
-		J1a <- Bessel::BesselJ(ka, 1)
-		E <- exp(-1 * kz)
-		if (radial.){
-			# radial displacements at the surface [ur(r,0)]
-			# Wang (2000) equation 9.29
-			J1 * J1a * E
-		} else {
-			# vertical displacements at the surface [uz(r,0)]
-			# Wang (2000) equation 9.30
-			J0 * J1 * E
-		}
-	}
-	
-surface_displacement_ringdisk <- function(x, radius, depth, thickness, p0=1, nu=1/4, ShearModulus=15e9, BiotCoef=1, x.lim, verbose=TRUE, tol_pow){
+#' @rdname segall92
+#' @param x 
+#' @param radius,depth,thickness numeric; the radius, midpoint depth, and thickness of the circular-disk pressure source; the
+#' midpoint-depth must be at least \code{thickness/2}
+#' @param p0 numeric; the (uniform) pressure change inside the circular-disk source
+#' @param nuu numeric; the undrained Poisson's ratio
+#' @param ShearModulus numeric; the elastic shear modulus
+#' @param BiotCoef numeric; Biot's coefficient (usually written as \eqn{\alpha})
+#' @param verbose logical; should messages be given?
+#' @param x.lim numeric; the limit of integration in the radial direction
+#' @param tol_pow numeric; the exponent applied to \code{.Machine$double.eps} used as the integration tolerance (see \code{\link{integrate}})
+#' @param nsub integer; the number of subdivisions in the integration (see \code{\link{integrate}})
+#' 
+#' @references Segall, P. (1992), Induced stresses due to fluid extraction from axisymmetric reservoirs,
+#' PAGEOPH, 139: 535. doi: 10.1007/BF00879950
+#' @export
+#' 
+#' @examples 
+#' 
+#' # Calculate surface displacements from a pressure-disk source
+#' 
+#' # Radial distances (e.g., observation points) and pressure source strength
+#' # (in this case, keep distances in km to stabilize integration
+#' #  and then rescale pressure to maintain unit consistency)
+#' r <- seq(0, 15, length.out=151)
+#' Pa <- 80e3 #Pa (N / m^2)
+#' pressure <- 2.5 * Pa * (1000^2)
+#' 
+#' # dimensions of inflating (pressure > 0) or deflating (pressure < 0) reservoir
+#' disk.radius <- 4
+#' disk.thickness <- 2
+#' disk.middepth <- 3
+#' 
+#' # calculations...
+#' res <- surface_displacement_ringdisk(r, radius = disk.radius, thickness = disk.thickness, depth = disk.middepth, p0 = pressure)
+#' head(res)
+#' 
+#' with(res,{
+#'   uz_sc <- -uz
+#'   ur_sc <- ur
+#'   yl <- range(c(uz_sc, ur_sc, err), na.rm=TRUE)
+#'   plot(x, uz_sc, col=NA, log='', ylim=yl, xaxs='i',
+#'        ylab="Displacement, mm", xlab="Distance from source, km", main="Surface Displacements: Pressure-disk Source")
+#'   abline(h=0, col='grey')
+#'
+#'   lines(x, uz_sc, lwd=1.5)
+#'   text(10, 7, "Vertical")
+#'
+#'   lines(x, ur_sc, lty=2, lwd=1.5)
+#'   text(5, 5, "Radial")
+#'
+#'   lines(x, err, lty=3, lwd=1.5)
+#'   text(4.5, -0.75, "Radial strain\n(mm/km)", pos=2)
+#'
+#'   mtext(sprintf("Segall (1992) model with radius: %s, Thickness: %s, Depth: %s", disk.radius, disk.thickness, disk.middepth), font=3)
+#' })
+#' 
+surface_displacement_ringdisk <- function(x, radius, depth, thickness, 
+                                          p0=1, nuu=1/4, ShearModulus=15e9, BiotCoef=1, verbose=TRUE, 
+                                          x.lim, tol_pow, nsub){
 
 	if (depth < thickness/2) stop("must be from: <depth - thickness/2>  to  <depth + thickness/2>")
 	
@@ -52,18 +104,18 @@ surface_displacement_ringdisk <- function(x, radius, depth, thickness, p0=1, nu=
 		as.numeric(x.lim)
 	}
 	
-	# Geetsma's uniaxial poroelastic coefficient
+	# Geetsma's uniaxial poroelastic coefficient (Young's modulus?)
 	# Wang (2000) 3.71
 	c_m <- BiotCoef / ShearModulus
 	
-	scaling <- 2 * c_m * (1 - nu) * p0 * thickness * radius
+	scaling <- 2 * c_m * (1 - nuu) * p0 * thickness * radius
 
 	# Integration parameters
-	nsub <- 101L
+	nsub <- ifelse(missing(nsub), 101L, as.integer(nsub))
 	tol <- .Machine$double.eps^ifelse(missing(tol_pow), 0.35, tol_pow)
 	
 	.fun <- function(r.., ...){
-		int <- integrate(.green_integ, lower=0, upper=x.lim, stop.on.error=FALSE, r. = r.., ..., subdivisions = nsub, rel.tol=tol)
+		int <- stats::integrate(.green_segall92, lower=0, upper=x.lim, stop.on.error=FALSE, r. = r.., ..., subdivisions = nsub, rel.tol=tol)
 		int[['value']]
 	}
 	   
diff --git a/README.md b/README.md
index 79e3aad..226896d 100644
--- a/README.md
+++ b/README.md
@@ -4,4 +4,14 @@ Tools for studying crustal deformation from natural and anthropogenic sources
 
 [![T-CI Build Status](https://travis-ci.org/abarbour/deform.svg?branch=master)](https://travis-ci.org/abarbour/deform) [![AppVeyor Build Status](https://ci.appveyor.com/api/projects/status/github/abarbour/deform?branch=master&svg=true)](https://ci.appveyor.com/project/abarbour/deform) [![Coverage Status](https://img.shields.io/codecov/c/github/abarbour/deform/master.svg)](https://codecov.io/github/abarbour/deform?branch=master)
 
-## Description
\ No newline at end of file
+## Description
+
+## Installation
+
+This is not yet on CRAN, so:
+
+```{r}
+if ('remotes' %in% rownames(installed.packages())) install.packages('remotes')
+library(remotes)
+remotes::install_github('abarbour/deform')
+```
diff --git a/man/segall92.Rd b/man/segall92.Rd
new file mode 100644
index 0000000..e98d7d9
--- /dev/null
+++ b/man/segall92.Rd
@@ -0,0 +1,83 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/segall92.R
+\name{segall92}
+\alias{segall92}
+\alias{surface_displacement_ringdisk}
+\title{Elastostatic subsidence of a half space}
+\usage{
+segall92()
+
+surface_displacement_ringdisk(x, radius, depth, thickness, p0 = 1,
+  nuu = 1/4, ShearModulus = 1.5e+10, BiotCoef = 1, verbose = TRUE,
+  x.lim, tol_pow, nsub)
+}
+\arguments{
+\item{x}{}
+
+\item{radius, depth, thickness}{numeric; the radius, midpoint depth, and thickness of the circular-disk pressure source; the
+midpoint-depth must be at least \code{thickness/2}}
+
+\item{p0}{numeric; the (uniform) pressure change inside the circular-disk source}
+
+\item{nuu}{numeric; the undrained Poisson's ratio}
+
+\item{ShearModulus}{numeric; the elastic shear modulus}
+
+\item{BiotCoef}{numeric; Biot's coefficient (usually written as \eqn{\alpha})}
+
+\item{verbose}{logical; should messages be given?}
+
+\item{x.lim}{numeric; the limit of integration in the radial direction}
+
+\item{tol_pow}{numeric; the exponent applied to \code{.Machine$double.eps} used as the integration tolerance (see \code{\link{integrate}})}
+
+\item{nsub}{integer; the number of subdivisions in the integration (see \code{\link{integrate}})}
+}
+\description{
+Elastostatic subsidence of a half space
+}
+\examples{
+
+# Calculate surface displacements from a pressure-disk source
+
+# Radial distances (e.g., observation points) and pressure source strength
+# (in this case, keep distances in km to stabilize integration
+#  and then rescale pressure to maintain unit consistency)
+r <- seq(0, 15, length.out=151)
+Pa <- 80e3 #Pa (N / m^2)
+pressure <- 2.5 * Pa * (1000^2)
+
+# dimensions of inflating (pressure > 0) or deflating (pressure < 0) reservoir
+disk.radius <- 4
+disk.thickness <- 2
+disk.middepth <- 3
+
+# calculations...
+res <- surface_displacement_ringdisk(r, radius = disk.radius, thickness = disk.thickness, depth = disk.middepth, p0 = pressure)
+head(res)
+
+with(res,{
+  uz_sc <- -uz
+  ur_sc <- ur
+  yl <- range(c(uz_sc, ur_sc, err), na.rm=TRUE)
+  plot(x, uz_sc, col=NA, log='', ylim=yl, xaxs='i',
+       ylab="Displacement, mm", xlab="Distance from source, km", main="Surface Displacements: Pressure-disk Source")
+  abline(h=0, col='grey')
+
+  lines(x, uz_sc, lwd=1.5)
+  text(10, 7, "Vertical")
+
+  lines(x, ur_sc, lty=2, lwd=1.5)
+  text(5, 5, "Radial")
+
+  lines(x, err, lty=3, lwd=1.5)
+  text(4.5, -0.75, "Radial strain\\n(mm/km)", pos=2)
+
+  mtext(sprintf("Segall (1992) model with radius: \%s, Thickness: \%s, Depth: \%s", disk.radius, disk.thickness, disk.middepth), font=3)
+})
+
+}
+\references{
+Segall, P. (1992), Induced stresses due to fluid extraction from axisymmetric reservoirs,
+PAGEOPH, 139: 535. doi: 10.1007/BF00879950
+}