Immediate question as follow up: How could I do that?
EDIT: If this is the way to go Measured values and graphing - Evaluating measured values in Checkmk quickly and easily then I suppose I would have to upgrade to some enterprise version (?)
EDIT 2: rrdtool? Found several *.rrd files in ~/var/pnp4nagios/perfdata/my-server. One for each metric. Full of cryptic stuff 
EDIT 3: rrdtools info service_name_rooms.rrd, for instance, shows a lot of stuff:
filename = "service_name_rooms.rrd"
rrd_version = "0003"
step = 60
last_update = 1677349452
header_size = 2872
ds[1].index = 0
ds[1].type = "GAUGE"
ds[1].minimal_heartbeat = 8460
ds[1].min = NaN
ds[1].max = NaN
ds[1].last_ds = "0"
ds[1].value = 0.0000000000e+00
ds[1].unknown_sec = 0
rra[0].cf = "AVERAGE"
rra[0].rows = 2880
rra[0].cur_row = 2572
rra[0].pdp_per_row = 1
rra[0].xff = 5.0000000000e-01
rra[0].cdp_prep[0].value = NaN
rra[0].cdp_prep[0].unknown_datapoints = 0
rra[1].cf = "AVERAGE"
rra[1].rows = 2880
rra[1].cur_row = 1788
rra[1].pdp_per_row = 5
rra[1].xff = 5.0000000000e-01
rra[1].cdp_prep[0].value = 0.0000000000e+00
rra[1].cdp_prep[0].unknown_datapoints = 0
rra[2].cf = "AVERAGE"
rra[2].rows = 4320
rra[2].cur_row = 495
rra[2].pdp_per_row = 30
rra[2].xff = 5.0000000000e-01
rra[2].cdp_prep[0].value = 0.0000000000e+00
rra[2].cdp_prep[0].unknown_datapoints = 0
rra[3].cf = "AVERAGE"
rra[3].rows = 5840
rra[3].cur_row = 93
rra[3].pdp_per_row = 360
rra[3].xff = 5.0000000000e-01
rra[3].cdp_prep[0].value = 0.0000000000e+00
rra[3].cdp_prep[0].unknown_datapoints = 0
rra[4].cf = "MAX"
rra[4].rows = 2880
rra[4].cur_row = 493
rra[4].pdp_per_row = 1
rra[4].xff = 5.0000000000e-01
rra[4].cdp_prep[0].value = NaN
rra[4].cdp_prep[0].unknown_datapoints = 0
rra[5].cf = "MAX"
rra[5].rows = 2880
rra[5].cur_row = 270
rra[5].pdp_per_row = 5
rra[5].xff = 5.0000000000e-01
rra[5].cdp_prep[0].value = 0.0000000000e+00
rra[5].cdp_prep[0].unknown_datapoints = 0
rra[6].cf = "MAX"
rra[6].rows = 4320
rra[6].cur_row = 2820
rra[6].pdp_per_row = 30
rra[6].xff = 5.0000000000e-01
rra[6].cdp_prep[0].value = 0.0000000000e+00
rra[6].cdp_prep[0].unknown_datapoints = 0
rra[7].cf = "MAX"
rra[7].rows = 5840
rra[7].cur_row = 2352
rra[7].pdp_per_row = 360
rra[7].xff = 5.0000000000e-01
rra[7].cdp_prep[0].value = 0.0000000000e+00
rra[7].cdp_prep[0].unknown_datapoints = 0
rra[8].cf = "MIN"
rra[8].rows = 2880
rra[8].cur_row = 2077
rra[8].pdp_per_row = 1
rra[8].xff = 5.0000000000e-01
rra[8].cdp_prep[0].value = NaN
rra[8].cdp_prep[0].unknown_datapoints = 0
rra[9].cf = "MIN"
rra[9].rows = 2880
rra[9].cur_row = 68
rra[9].pdp_per_row = 5
rra[9].xff = 5.0000000000e-01
rra[9].cdp_prep[0].value = 0.0000000000e+00
rra[9].cdp_prep[0].unknown_datapoints = 0
rra[10].cf = "MIN"
rra[10].rows = 4320
rra[10].cur_row = 4029
rra[10].pdp_per_row = 30
rra[10].xff = 5.0000000000e-01
rra[10].cdp_prep[0].value = 0.0000000000e+00
rra[10].cdp_prep[0].unknown_datapoints = 0
rra[11].cf = "MIN"
rra[11].rows = 5840
rra[11].cur_row = 4228
rra[11].pdp_per_row = 360
rra[11].xff = 5.0000000000e-01
rra[11].cdp_prep[0].value = 0.0000000000e+00
rra[11].cdp_prep[0].unknown_datapoints = 0
I have the feeling, changes would have to be made here and then “updated”. Just how, is the question…