pp.timeplot <-
function (x, div = "year", type = "l", xlab = "", xnam = NULL, 
    ...) 
{
    if (is.data.frame(x)) 
        x <- as.matrix(x)
    if (is.matrix(x)) {
        matplot(x, axes = FALSE, type = type, xlab = xlab, ...)
        if (!length(xnam)) {
            xnam <- row.names(x)
        }
        else if (length(xnam) != nrow(x)) {
            stop("'xnam' is the wrong length")
        }
    }
    else {
        plot(x, axes = FALSE, type = type, xlab = xlab, ...)
        if (!length(xnam)) {
            xnam <- names(x)
        }
        else if (length(xnam) != length(x)) {
            stop("'xnam' is the wrong length")
        }
    }
    axis(2)
    if (!is.character(div) || length(div) != 1) {
        stop("'div' must be a single character string -- given has mode ", 
            mode(div), " and length ", length(div))
    }
    div.menu <- c("years", "decades", "months")
    div.num <- pmatch(div, div.menu, nomatch = 0)
	if(div.num == 0) {
		stop("unknown or ambiguous value given for 'div' -- possible ",
			"values are: ", paste(div.menu, collapse=", "))
	}
	div <- div.menu[div.num]
    switch(div, decades = {
        tim <- substring(xnam, 1, 3)
        tlab <- paste(unique(tim), "0's", sep = "")
    }, years = {
        tim <- substring(xnam, 1, 4)
        tlab <- unique(tim)
    }, months = {
		tim <- substring(xnam, 1, 7)
		tlab <- substring(unique(tim), 6, 7)
	})
    tcount <- cumsum(table(tim))
    tbrk <- tcount[-length(tcount)] + 0.5
    axis(1, at = tbrk, labels = rep("", length(tbrk)), tck = 1, 
        lty = 2, col = 2)
    axis(1, at = tbrk, labels = rep("", length(tbrk)), lty = 2, 
        col = 2)
    maxd <- max(diff(tcount))
    tcount[length(tcount)] <- tcount[length(tcount) - 1] + maxd
    axis(1, at = tcount - maxd/2, labels = tlab, tck = 0)
    box()
}