dtick

Sets the step in-between ticks on this axis. Use with tick0. Must be a positive number, or special strings available to "log" and "date" axes. If the axis type is "log", then ticks are set every 10^(n"dtick) where n is the tick number. For example, to set a tick mark at 1, 10, 100, 1000, ... set dtick to 1. To set tick marks at 1, 100, 10000, ... set dtick to 2. To set tick marks at 1, 5, 25, 125, 625, 3125, ... set dtick to log_10(5), or 0.69897000433. "log" has several special values; "L", where f is a positive number, gives ticks linearly spaced in value (but not position). For example tick0 = 0.1, dtick = "L0.5" will put ticks at 0.1, 0.6, 1.1, 1.6 etc. To show powers of 10 plus small digits between, use "D1" (all digits) or "D2" (only 2 and 5). tick0 is ignored for "D1" and "D2". If the axis type is "date", then you must convert the time to milliseconds. For example, to set the interval between ticks to one day, set dtick to 86400000.0. "date" also has special values "M" gives ticks spaced by a number of months. n must be a positive integer. To set ticks on the 15th of every third month, set tick0 to "2000-01-15" and dtick to "M3". To set ticks every 4 years, set dtick to "M48"