Look for the gray patches on the white background. You should see all patches labeled 223 through 254. If high values (250-254) blend into white, your monitor is clipping highlights - reduce contrast or check the OSD.
Fullscreen
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
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