diff --git a/coordinator/renderer.lua b/coordinator/renderer.lua
index d64ca98..c41f46c 100644
--- a/coordinator/renderer.lua
+++ b/coordinator/renderer.lua
@@ -15,10 +15,12 @@ local panel_view = require("coordinator.ui.layout.front_panel")
 local main_view  = require("coordinator.ui.layout.main_view")
 local unit_view  = require("coordinator.ui.layout.unit_view")
 
+local core       = require("graphics.core")
 local flasher    = require("graphics.flasher")
 
 local DisplayBox = require("graphics.elements.displaybox")
 
+---@class coord_renderer
 local renderer = {}
 
 -- render engine
@@ -177,35 +179,46 @@ function renderer.close_fp()
 end
 
 -- start the coordinator GUI
-function renderer.start_ui()
+---@return boolean success, any error_msg
+function renderer.try_start_ui()
+    local status, msg = true, nil
+
     if not engine.ui_ready then
         -- hide dmesg
         engine.dmesg_window.setVisible(false)
 
-        -- show main view on main monitor
-        if engine.monitors.primary ~= nil then
-            engine.ui.main_display = DisplayBox{window=engine.monitors.primary,fg_bg=style.root}
-            main_view(engine.ui.main_display)
+        status, msg = pcall(function ()
+            -- show main view on main monitor
+            if engine.monitors.primary ~= nil then
+                engine.ui.main_display = DisplayBox{window=engine.monitors.primary,fg_bg=style.root}
+                main_view(engine.ui.main_display)
+            end
+
+            -- show flow view on flow monitor
+            if engine.monitors.flow ~= nil then
+                engine.ui.flow_display = DisplayBox{window=engine.monitors.flow,fg_bg=style.root}
+                flow_view(engine.ui.flow_display)
+            end
+
+            -- show unit views on unit displays
+            for idx, display in pairs(engine.monitors.unit_displays) do
+                engine.ui.unit_displays[idx] = DisplayBox{window=display,fg_bg=style.root}
+                unit_view(engine.ui.unit_displays[idx], idx)
+            end
+        end)
+
+        if status then
+            -- start flasher callback task and report ready
+            flasher.run()
+            engine.ui_ready = true
+        else
+            -- report fail and close ui
+            msg = core.extract_assert_msg(msg)
+            renderer.close_ui()
         end
-
-        -- show flow view on flow monitor
-        if engine.monitors.flow ~= nil then
-            engine.ui.flow_display = DisplayBox{window=engine.monitors.flow,fg_bg=style.root}
-            flow_view(engine.ui.flow_display)
-        end
-
-        -- show unit views on unit displays
-        for idx, display in pairs(engine.monitors.unit_displays) do
-            engine.ui.unit_displays[idx] = DisplayBox{window=display,fg_bg=style.root}
-            unit_view(engine.ui.unit_displays[idx], idx)
-        end
-
-        -- start flasher callback task
-        flasher.run()
-
-        -- report ui as ready
-        engine.ui_ready = true
     end
+
+    return status, msg
 end
 
 -- close out the UI
diff --git a/coordinator/startup.lua b/coordinator/startup.lua
index 145f77b..cf902fc 100644
--- a/coordinator/startup.lua
+++ b/coordinator/startup.lua
@@ -22,7 +22,7 @@ local sounder     = require("coordinator.sounder")
 
 local apisessions = require("coordinator.session.apisessions")
 
-local COORDINATOR_VERSION = "v1.0.14"
+local COORDINATOR_VERSION = "v1.0.15"
 
 local println = util.println
 local println_ts = util.println_ts
@@ -198,9 +198,8 @@ local function main()
 
         local draw_start = util.time_ms()
 
-        local ui_ok, ui_message = pcall(renderer.start_ui)
+        local ui_ok, ui_message = renderer.try_start_ui()
         if not ui_ok then
-            renderer.close_ui()
             log_graphics(util.c("main UI error: ", ui_message))
             log.fatal(util.c("main GUI render failed with error ", ui_message))
         else
diff --git a/graphics/core.lua b/graphics/core.lua
index 88e0f30..2f17d98 100644
--- a/graphics/core.lua
+++ b/graphics/core.lua
@@ -115,7 +115,7 @@ end
 
 -- extract the custom element assert message, dropping the path to the element file
 function core.extract_assert_msg(msg)
-    local start = string.find(msg, "@") or 1
+    local start = (string.find(msg, "@") + 1) or 1
     return string.sub(msg, start)
 end
 
diff --git a/graphics/elements/indicators/rad.lua b/graphics/elements/indicators/rad.lua
index 5987625..d13655e 100644
--- a/graphics/elements/indicators/rad.lua
+++ b/graphics/elements/indicators/rad.lua
@@ -10,7 +10,7 @@ local element = require("graphics.element")
 ---@field format string data format (lua string format)
 ---@field commas? boolean whether to use commas if a number is given (default to false)
 ---@field lu_colors? cpair label foreground color (a), unit foreground color (b)
----@field value number default value
+---@field value? radiation_reading default value
 ---@field parent graphics_element
 ---@field id? string element id
 ---@field x? integer 1 if omitted
@@ -24,7 +24,6 @@ local element = require("graphics.element")
 ---@param args rad_indicator_args
 ---@return graphics_element element, element_id id
 local function rad(args)
-    element.assert(type(args.value) ~= "number", "value is a required number field")
     element.assert(type(args.label) == "string", "label is a required field")
     element.assert(type(args.format) == "string", "format is a required field")
     element.assert(util.is_int(args.width), "width is a required field")